Preheat oven to 350°F.
In a skillet, cook the ground beef and onion until beef is browned and onion is tender.
Drain excess fat.
Stir in the tomato sauce and Ro-Tel tomatoes.
Pour the beef mixture into a 9x13 inch baking dish.
Prepare the Jiffy corn muffin mix according to package instructions.
Spread the corn muffin batter over the beef mixture.
Sprinkle the shredded cheddar cheese on top.
Bake for 30 minutes or until the corn muffin topping is golden brown.
