Cooking Day: Place beef and ingredients for marinade (garlic, oil, soy sauce, Worcestershire sauce, Dijon mustard, lemon juice and pepper) into a Ziploc bag. Freeze.
Serving Day: Assemble skewers, alternating meat with onions, peppers, tomatoes and mushrooms.
Grill 3 minutes per side, turning and basting often with marinade as cooking.