Preheat your oven to 350°F (175°C).
In a large pot, cook the spaghetti according to package instructions until al dente. Drain and set aside.
In a skillet over medium heat, melt the butter. Add the sliced mushrooms and sauté until cooked, about 5 minutes.
Stir in the flour and cook for 1 minute to create a roux.
Gradually whisk in the chicken broth and milk, stirring continuously until the sauce thickens, about 3-5 minutes.
Add the garlic powder, onion powder, salt, and pepper to the sauce. Mix well.
In a large bowl, combine the cooked spaghetti, chicken, peas, and mushroom sauce. Mix until everything is well coated.
Transfer the mixture to a greased 9x13 inch baking dish. Top with shredded cheddar cheese, Parmesan cheese, and breadcrumbs.
Bake in the preheated oven for about 25-30 minutes, or until the top is golden and bubbly.
Remove from the oven and let it sit for a few minutes before serving.