Heat oven to 350°. Shred beef into small pieces. In hot vegetable oil, sauté the onion, pepper and garlic until softened, 3 to 4 minutes. Add the beef, rice, tomatoes and green chilies and taco seasoning. Transfer to a 3-quart casserole dish and bake until bubbling hot, about 15 minutes. Sprinkle with cheese and bake until cheese melts, 2 to 3 minutes.