Preheat your oven to 350°F (175°C). Grease a 9x13 inch baking dish with cooking spray or a little olive oil.

In a large skillet, heat the olive oil over medium heat. Add the diced onion and bell pepper, and sauté until softened, about 5 minutes.

In a large mixing bowl, combine the cooked spaghetti, shredded chicken, diced tomatoes with green chilies, cream of chicken soup, half of the cheddar cheese, half of the Monterey Jack cheese, sautéed onion and bell pepper, garlic powder, paprika, cayenne pepper, salt, and pepper. Mix well until all ingredients are evenly incorporated.

Pour the mixture into the prepared baking dish and spread it out evenly. Top with the remaining cheddar and Monterey Jack cheeses, and sprinkle the sliced black olives on top if using.

Cover the baking dish with aluminum foil and bake for 25 minutes. Remove the foil and bake for an additional 15 minutes, or until the cheese is bubbly and golden brown.

Once done, remove from the oven and let it cool for about 5 minutes. Garnish with chopped fresh parsley before serving.