In a large skillet, heat olive oil over medium heat. Add the diced onion and bell pepper. Sauté until softened, about 5-7 minutes.
In a large mixing bowl, combine the cooked spaghetti, shredded chicken, cream of mushroom soup, chicken broth, garlic powder, paprika, salt, and pepper. Mix well until all ingredients are evenly coated.
Add the sautéed onion and bell pepper mixture to the bowl and stir until combined.
Transfer the mixture into a greased 9x13 inch baking dish, spreading it evenly.
Sprinkle the shredded cheddar cheese on top in an even layer.
Bake in the preheated oven for 25-30 minutes or until the cheese is bubbly and golden.
Remove from the oven and let cool for a few minutes before serving.