Shepherd's Pie I

Heat oil in frying pan. Add chopped onions, and fry until golden brown. Add ground beef, and keep stirring until meat is browned. Add crushed tomatoes, and continue to cook until liquid from the tomatoes evaporates. Salt to taste.
In the meantime, prepare the mashed potatoes as directed on the packet.
Spread the meat mixture into the bottom of an oven proof dish. Cover with a layer of mashed potatoes, and top with grated cheese.
Bake for 10 minutes at 400 degrees F (205 degrees C), or until cheese has melted and browned.