Begin by bringing a large pot of salted water to a boil. 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 chopped onion and bell pepper, cooking for 5-7 minutes until tender and slightly browned.

Incorporate cream of chicken soup and sour cream into the skillet with the sautéed vegetables. Add garlic powder, onion powder, and milk. Stir for 2-3 minutes until smooth and creamy.

Fold in shredded cooked chicken and pour in half of the Monterey Jack cheese. Stir for 2-3 minutes until the cheese melts and the mixture is gooey.

Add the drained spaghetti to the skillet and toss gently to coat the pasta with the creamy chicken mixture.

For an optional baked finish, preheat the oven to 350°F. Transfer to a greased baking dish, top with remaining cheeses, and bake for 20-25 minutes until cheese is melted and bubbling.

Remove from oven, let cool for a few minutes, garnish with parsley if desired, and serve warm.