Creamy chicken spaghetti baked with Velveeta and Rotel tomatoes is a beloved Southern family casserole. This chicken dish is protein-rich, crowd-pleasing, and a guaranteed potluck hit.
Bring a large pot of water to a boil and cook spaghetti according to package directions until just al dente; drain and set aside.
While pasta cooks, heat 2 tbsp olive oil over medium-high in a large skillet. Sauté diced onion and green bell pepper until softened, about 4 minutes.
Add chicken breast to the skillet, season with salt, pepper, and garlic powder, and cook for 8–10 minutes, turning occasionally, until fully cooked. Allow chicken to rest briefly, then shred or dice.
In a separate pot, add Velveeta, Rotel tomatoes (with juices), and cream of mushroom soup. Stir over medium-low heat until cheese is melted and mixture is creamy.
Combine cooked spaghetti, sautéed vegetables, shredded chicken, and cheese sauce in a large bowl. Toss thoroughly, then transfer mixture to a greased 9x13-inch baking dish.
Bake uncovered at 350°F (175°C) for 25 minutes, until the top is golden and casserole is bubbling. Let rest 5 minutes before serving.