Bring a large pot of salted water to a boil. Add spaghetti and cook until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Sauté onion, bell pepper, and mushrooms for 5-7 minutes until onions are translucent.

Stir in cream of chicken soup, sour cream, garlic powder, and onion powder. Mix until smooth, then add milk. Cook for 2-3 minutes until heated through.

Add cooked chicken and Monterey Jack cheese to the skillet. Stir until combined and cheese melts, about 2-3 minutes.

Add cooked spaghetti to the skillet and toss until evenly coated with the sauce.

For a baked version, preheat oven to 350°F (175°C). Transfer mixture to a greased baking dish, top with remaining cheeses, and bake for 20-25 minutes until bubbly.

Let cool slightly before serving. Garnish with parsley and serve warm.