Slice Chicken Breast:

Slice the chicken breast horizontally into two pieces of even thickness.

Season Both Sides:

Apply salt, pepper, and Italian seasoning to both sides of the chicken.

Sear Chicken in Oil:

Warm olive oil in a large pot over medium-high heat. Place the chicken in the pot and cook for 5-6 minutes per side until golden and fully cooked.

Rest and Dice Chicken:

Remove the chicken and let it rest for 10 minutes, then dice into bite-sized chunks. Return any released juices to the pot.

Preheat Oven to 350°F:

Set the oven to 350°F (175°C).

Deglaze with Wine:

In the same pot over medium heat, melt the butter. Add the white wine and use a silicone spatula to deglaze the bottom. Allow the wine to simmer for 5 minutes to reduce.

Sauté Mushrooms and Onion:

Add the diced mushrooms and onion; sauté for 5 minutes, stirring now and then. Stir in the garlic and cook for an additional 1 minute.

Add Cream and Chicken:

Lower the heat to medium-low. Mix in the cream of chicken soup, cream of mushroom soup, Parmesan, sour cream, milk, frozen peas, and diced chicken. Cook, stirring occasionally, until everything is hot.

Boil Spaghetti Al Dente:

In the meantime, boil the spaghetti in salted water until al dente, roughly 10 minutes. Drain thoroughly.

Combine Pasta and Sauce:

Put the drained spaghetti back into the pot. Pour the warm sauce over the pasta and mix well.

Transfer to Baking Dish:

Move the pasta mixture to a 9x13-inch baking dish or a large oven-safe pot. Spread the mozzarella cheese evenly on top.

Bake with Mozzarella:

Bake uncovered at 350°F (175°C) for 15 minutes. Then raise the oven temperature to 450°F (230°C) and bake for another 10 minutes, until the top is bubbling and lightly browned.

Rest and Garnish:

Allow the casserole to sit for 5 minutes. Sprinkle fresh parsley on top and serve.