1. Place the meat strips in a large skillet.
2. Brown the meat on both sides, remove and set aside.
3. Place the tomato sauce and Worcestershire sauce in a bowl.
4. Mix well.
5. Stir in the brown sugar, mustard, water and pepper until well blended and the brown sugar is completely dissolved.
6. Place the meat strips back in the skillet.
7. Pour the sauce over the top of the meat.
8. Spread the onion slices over the top.
9. Cook on low temperature, covered for 20 minutes or until heated through.