Preheat your oven to 350°F (175°C). Lightly grease a 9×13-inch baking dish.

In a large skillet, melt the butter over medium heat. Add diced onions and cook until softened, about 5 minutes.

Add minced garlic and sliced mushrooms to the skillet, cooking until the mushrooms are tender.

Sprinkle the flour over the vegetables, stirring constantly to form a roux. Cook for 1-2 minutes until the flour is lightly browned.

Gradually whisk in the chicken broth and heavy cream. Continue to cook, stirring constantly, until the sauce thickens.

Stir in the grated Parmesan cheese, dry white wine (if using), and season with salt and pepper to taste.

Add the cooked, shredded chicken, thawed peas, and cooked spaghetti to the sauce, stirring to combine.

Pour the mixture into the prepared baking dish, spreading it out evenly.

Sprinkle the shredded mozzarella cheese and breadcrumbs evenly over the top.

Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is golden brown.

Remove from the oven and let it cool for a few minutes before serving. Garnish with chopped fresh parsley, if desired.

Prep Time: 20 minutes