Heat oven to 375° F. In a large skillet combine oil, onion, green pepper, garlic, and ground beef. Sauté until vegetables are tender and beef is nearly brown. Add all remaining ingredients except cheese and stir until spaghetti is well-blended. Place mixture into a lightly-greased 2-quart casserole and sprinkle with cheese. Bake for 30 minutes or until cheese is melted and bubbly.