Cook pasta. In a large skillet, saute onion and pepper in oil until tender. Add chicken, Cajun seasoning ang garlic; heat through. Transfer to a large bowl. Drain pasta; add to chicken mix. Stir in Alfredo and spaghetti sauce.
Transfer to a greased 13x9 baking dish. Sprinkle with cheeses. Cover and bake at 375 for 15 min, uncover and bake for 10-15 min longer.