Preheat your oven to 350°F (175°C).
Cook the spaghetti according to package instructions until al dente.
In a large skillet, heat olive oil over medium heat. Add sliced mushrooms and sauté until soft.
Add cooked chicken and frozen peas to the skillet, stirring well.
Pour in chicken broth and heavy cream, adding garlic powder, salt, and pepper. Stir to combine.
Gently fold the cooked spaghetti into the mixture, ensuring it’s well-coated.
Transfer the mixture into a greased 9x13-inch baking dish.
Sprinkle grated Parmesan cheese over the top of the casserole.
Bake in the preheated oven for 25-30 minutes or until bubbly and golden brown.
Remove from the oven and let it cool for a few minutes before serving.
