Preheat your oven to 350°F (175°C).
Cook spaghetti in a large pot of salted boiling water until just al dente. Drain and set aside.
In a large skillet, melt butter over medium heat. Add onion and bell pepper and sauté until soft, about 5 minutes.
In a large bowl, stir together cream of chicken soup, Rotel, sour cream, garlic powder, and shredded cheddar cheese.
Add the sautéed veggies, shredded chicken, and cooked spaghetti to the bowl and mix until combined. Season with salt and pepper.
Pour everything into a greased 9x13-inch baking dish. Top with a little extra cheese if you're feeling it.
Bake for 25-30 minutes, or until bubbly and golden on top.
Serve hot, maybe with a green salad if you’re feeling fancy.