Bring a large pot of salted water to a boil. Once boiling, add spaghetti and cook according to package instructions until al dente, about 8-10 minutes. Drain and set aside.

In a large skillet, heat olive oil over medium heat. Add onion, bell pepper, and mushrooms, stirring for 5-7 minutes until softened and slightly browned.

Stir in cream of chicken soup, sour cream, garlic powder, onion powder, and milk (or broth) to the sautéed vegetables. Cook on low for 2-3 minutes until heated through and well combined.

Mix in shredded cooked chicken and Monterey Jack cheese until well combined. Cook for another 2-3 minutes over low heat until the cheese is fully melted.

Add drained spaghetti to the skillet, tossing until well-coated in the creamy sauce, ensuring an even distribution of ingredients.

For a baked version, preheat oven to 350°F (175°C). Transfer pasta mixture to a greased baking dish, top with remaining Monterey Jack and cheddar cheese. Bake for 20-25 minutes until bubbly and golden.

Let cool for a few minutes. Garnish with freshly chopped parsley before serving warm.