Pin It The first time I made this casserole, I was trying to use up leftover rotisserie chicken from a weekend gathering. My kitchen smelled incredible as the mushrooms and onions hit the hot olive oil, that earthy aroma filling every corner of the room. I honestly threw everything together without measuring, hoping it would work, and my roommate kept wandering in asking what was baking. When we finally sat down to eat, the way the creamy sauce had melded with the tender chicken and vegetables felt like something Id spent hours perfecting.
Last winter my sister came over for dinner after a long week at work. She walked in while this was in the oven and immediately asked what I was making because the cheese had started to bubble and brown. We sat at the counter with our bowls, steam rising into the cool kitchen air, and she admitted shed been eating takeout for days because she was too tired to cook something comforting. Watching her shoulders actually relax as she took that first bite made me realize how much we need food that feels like a hug.
Ingredients
- 2 cups cooked chicken breast: Rotisserie chicken saves so much time and already has that seasoned flavor baked right in
- 4 cups fresh spinach: It wilts down dramatically in the pan so do not be afraid of the huge amount at first
- 2 cups mushrooms: Button mushrooms work fine but cremini add this deeper earthy flavor that really shines
- 1 small onion: Finely chopping ensures they disappear into the sauce instead of staying in distinct pieces
- 3 cloves garlic: Add it right at the end so it does not burn and turn bitter in the hot pan
- 1 cup mozzarella cheese: Shredding it yourself melts better than the pre-shredded bags with anti-caking agents
- 1/4 cup parmesan cheese: This adds a salty sharpness that cuts through the rich cream
- 1/2 cup heavy cream: Do not substitute with milk or the sauce will not thicken properly in the oven
- 2 tablespoons olive oil: You need enough fat to properly sauté the mushrooms or they will steam instead of brown
- 1 teaspoon Italian seasoning: Make your own blend with dried oregano, basil, and thyme for the freshest taste
- Salt and pepper: Taste the vegetable mixture before layering it since the parmesan will add more salt later
Instructions
- Get your oven ready:
- Preheat to 375°F and grab a 9x13 inch dish, giving it a quick coat of oil so nothing sticks later.
- Sauté the vegetables:
- Heat olive oil in a large skillet over medium heat, then cook onions and mushrooms for 5 to 7 minutes until they soften and turn golden brown.
- Add the aromatics:
- Stir in the garlic for just one minute until fragrant, then toss in all that spinach and watch it wilt down.
- Season it well:
- Sprinkle in salt, pepper, and Italian seasoning, tasting and adjusting before you remove it from the heat.
- Start the layers:
- Spread your cooked chicken across the bottom of your prepared dish in an even layer.
- Add the vegetables:
- Spoon the mushroom and spinach mixture over the chicken, spreading it out so every bite gets some.
- Pour on the cream:
- Drizzle the heavy cream evenly over everything, letting it seep down through the layers.
- Cheese time:
- Sprinkle both cheeses across the top, covering everything in that cheesy blanket.
- Bake it:
- Slide it into the oven for 20 to 25 minutes until the cheese is melted and bubbling with golden spots.
- The hardest part:
- Let it rest for 5 minutes before serving so the sauce has time to thicken up slightly.
Pin It 
This dish became my go-to when my neighbor had surgery last year. I dropped off a container still warm from the oven, and she texted me two days later saying it was the first thing she had actually wanted to eat since getting home from the hospital. Something about that combination of protein and vegetables in a creamy sauce just feels nourishing in a way that goes beyond nutrition.
Making It Ahead
You can assemble the entire casserole up to 24 hours before baking, just cover it tightly and keep it in the refrigerator. When you are ready to bake, you might need to add 5 to 10 minutes to the cooking time since it will be cold. The flavors actually meld together even better when they have that time to sit.
Freezing Instructions
Wrap the unbaked casserole tightly with plastic wrap and foil, then freeze for up to 3 months. Thaw overnight in the refrigerator before baking as directed. I have also baked it first, then frozen individual portions which reheat in the microwave in about 3 minutes.
Serving Ideas
This is plenty filling on its own, but sometimes I serve it with a simple arugula salad dressed with lemon vinaigrette to cut through the richness. Cauilfower rice also works beautifully if you want something that feels like a grain without the carbs.
- Crushed pork rinds make an incredible low-carb topping instead of extra cheese
- A splash of white wine in the vegetable mixture adds brightness
- Fresh basil on top right before serving pops against the golden cheese
Pin It There is something so satisfying about a dish that comes together quickly but tastes like you spent all day cooking it. This is the kind of recipe that makes low-carb eating feel like a treat instead of a compromise.
Recipe Questions & Answers
- → Can I use raw chicken instead of cooked?
Yes, but you'll need to adjust the cooking time. Brown cubed raw chicken in the skillet first, then set aside while you sauté the vegetables. Continue with the recipe as written, adding an extra 5-10 minutes of baking time to ensure the chicken cooks through completely.
- → How do I prevent the casserole from being watery?
The key is thoroughly sautéing the mushrooms and spinach until they release their moisture and the liquid evaporates. Also, avoid overcrowding the skillet when cooking vegetables. Patting cooked chicken dry before layering helps prevent excess liquid in the final dish.
- → Can I freeze this casserole?
Yes, assemble the entire casserole, cover tightly with foil and plastic wrap, then freeze for up to 3 months. Thaw overnight in the refrigerator before baking. Alternatively, bake first, then freeze individual portions for quick reheating.
- → What vegetables can I substitute for spinach?
Kale, Swiss chard, or broccoli florets work well as substitutes. For kale, remove the tough stems and chop finely. Broccoli may need slightly longer cooking time, so consider steaming it briefly before adding to the casserole.
- → Is this dish keto-friendly?
Yes, with only 6 grams of carbohydrates per serving, this casserole fits well into a ketogenic diet. The combination of protein from chicken and healthy fats from cheese and cream makes it satiating while keeping carbs low. Always verify your specific ingredients meet your dietary requirements.
- → How can I make this dairy-free?
Substitute heavy cream with full-fat coconut cream or unsweetened almond milk thickened with a bit of almond flour. Use dairy-free cheese alternatives or nutritional yeast for cheesy flavor. Note that texture and melting properties may vary.