In a medium size skillet add ground beef and chopped onions. Cook over medium heat until meat is lightly browned. Drain.
Add can of tomato sauce Worcestershire sauce, brown sugar and mustard and stir. Heat until boiling then remove from heat.
In a bowl, add box of cornbread mix, milk, egg and oil. Stir until all mix is moistened.
Spoon beef mixture into an 8x8 casserole dish. Top meat mixture with the shredded cheese. Bake at 350 for 25 to 30 minutes or until toothpick inserted into cornbread comes out clean.