1. Preheat your oven to 375°F (190°C). Lightly grease a 9×13-inch baking dish with olive oil or butter.
2. In a large skillet, heat olive oil over medium heat. Add chopped onions and sauté for about 3 minutes until translucent.
3. Add minced garlic and sliced mushrooms. Cook for another 5 minutes until mushrooms soften and release their juices.
4. Stir in chopped spinach and cook until just wilted, about 2 minutes. Remove from heat.
5. In a large bowl, combine cooked pasta, shredded chicken, sautéed veggies, cream of mushroom soup, sour cream, milk, smoked paprika, dried thyme, salt, and pepper. Mix gently until well incorporated.
6. Fold in 1 cup of cheddar and 1/2 cup mozzarella cheese, reserving the rest for topping.
7. Pour the mixture into the prepared baking dish, spreading evenly.
8. Sprinkle the remaining cheese and Parmesan (if using) on top for a golden, bubbly crust.
9. Bake uncovered for 25-30 minutes or until the cheese is melted and lightly browned on top. You’ll know it’s done when the edges are bubbly and the aroma fills your kitchen—just like Mama Lou’s place on a Sunday afternoon.
10. Let the casserole rest for 5 minutes before serving. This helps it set and makes it easier to slice.

One tip I learned from Ouma is to prepare the casserole earlier in the day and refrigerate it. When you pop it in the oven later, the flavors meld beautifully. It’s a simple trick that makes weeknight dinners feel like a special occasion.