Fillet the shark, remove the rather leathery skin, and divide the fish into 4 pieces, or buy shark steaks, ready to cook. Fry the tomato and onion in 1 tsp oil for 3 minutes to prepare a simple sauce. In another skillet, heat 3 Tbs oil over moderate heat. Dip the shark pieces into the flour and then coat them with beaten egg. Brown in the oil for 3 minutes on each side. Drain breifly on a paper towel. Serve warm, pouring the sauce over the pieces.