Step 1

Preheat the oven to 375°F (190°C).

Step 2

Heat ½ tablespoon of olive oil in a 10-inch skillet on medium-high heat.

Step 3

While the oil is heating, season the chicken pieces with ⅛ teaspoon of salt and the black pepper.

Step 4

Place the chicken pieces in the pan and brown on both sides, about 1 to 2 minutes. Remove the chicken pieces from the pan and transfer them to a bowl or a plate.Pro Tip: The chicken does not have to be cooked through. The chicken pieces will continue to cook in the oven.

Step 5

Add ½ tablespoon of olive oil to the pan and lower the heat to medium. Add the onions and cook until translucent, stirring frequently for about 2 minutes. Add the garlic and cook for an additional 30 seconds, stirring frequently.

Step 6

Raise the heat to medium-high and add the sliced mushrooms. Cook the mushrooms, stirring occasionally for 2 minutes.

Step 7

Pour the chicken broth into the pan and stir.

Step 8

Remove the pan from the heat and stir in the sour cream, heavy cream, Italian seasoning, cheddar cheese, mozzarella cheese, and remaining ⅛ teaspoon of salt.

Step 9

Add the chicken and cooked spaghetti to the pan and toss to coat.

Step 10

Pour the mixture into a lightly greased 5x5-inch baking dish. Place the dish on a rimmed baking sheet to catch any possible spills.

Step 11

Cover the casserole tightly with aluminum foil and bake for 20 to 25 minutes.

Step 12

Remove from the oven, top with shredded or grated Parmesan cheese and fresh chopped parsley if desired, and enjoy hot.