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

In a large skillet, heat 1 tablespoon of olive oil over medium heat. Add chopped onion, bell pepper, and sliced mushrooms. Sauté for 5-7 minutes until softened and onions are translucent.

Add cream of chicken soup, sour cream, garlic powder, onion powder, and milk to the skillet with the vegetables. Stir and heat for 2-3 minutes until smooth and slightly bubbling.

Fold in shredded cooked chicken and Monterey Jack cheese into the creamy sauce. Stir for 3-4 minutes until cheese melts and chicken is heated through.

Add the drained spaghetti to the skillet and toss everything together gently for about 2-3 minutes until well-coated with sauce.

For a crispy top, preheat the oven to 350°F (175°C). Transfer to a greased baking dish, sprinkle remaining Monterey Jack and cheddar cheese on top. Bake for 20-25 minutes until cheese is bubbly and golden.

Let cool for a few minutes, garnish with freshly chopped parsley, and serve warm with garlic bread or a green salad.