Place the steaks between sheets of wax paper, then pound until each steak is about ΒΌ inch thick.
Place the pounded steaks in a zip lock plastic bag. Add the mustard, cumin, garlic, olive oil, salt and pepper. Refrigerate for 3 hours or overnight. Be sure the steaks are evenly covered.
In a large skillet, heat the butter over medium heat. Add the onions and cook for about 10 minutes. Add the tomato, worcestershire sauce, wine, salt and pepper. Continue cooking for about 10 minutes more, stirring occasionally.
In a large skillet, heat the oil over medium heat. Place the steaks into the skillet and cook for 5 minutes per side. Add the onion sauce, mix and serve.