Preheat your oven to 350°F (175°C).
In a large skillet, heat the olive oil over medium heat. Add the chicken pieces and season with garlic powder, onion powder, smoked paprika, salt, and pepper. Cook until the chicken is browned and cooked through, about 5-7 minutes.
In a large mixing bowl, combine the cooked spaghetti, cooked chicken, barbecue sauce, half of the Monterey Jack cheese, green onions, and red bell pepper. Mix well until all ingredients are evenly coated.
Transfer the mixture to a greased 9x13-inch baking dish. Spread it out evenly and top with the remaining Monterey Jack cheese.
Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.
Remove from the oven and let it cool for a few minutes before serving.