Preheat your oven to 375°F (190°C).

In a large pot, cook the spaghetti according to package instructions. Drain and set aside.

Season the chicken breasts with salt, pepper, garlic powder, paprika, and cayenne pepper (if using).

In a large skillet, heat olive oil over medium-high heat. Add the seasoned chicken and cook for 6-7 minutes on each side, or until fully cooked and no longer pink in the center. Remove from skillet and let rest for a few minutes before slicing.

In the same skillet, add the diced red and green bell peppers and onion. Sauté for about 3-4 minutes until softened.

In a large mixing bowl, combine the cooked spaghetti, sautéed vegetables, barbecue sauce, and half of the Monterey Jack cheese. Mix well to combine.

Transfer the spaghetti mixture to a greased 9x13 inch baking dish. Top with sliced chicken and sprinkle the remaining Monterey Jack cheese on top.

Bake in the preheated oven for 20-25 minutes, or until the cheese is melted and bubbly.

Remove from the oven and let cool for a few minutes. Garnish with fresh parsley if desired before serving.