Brown ground beef in a large skillet over medium-high heat.
Drain any grease. Add Worcestershire sauce, ketchup, minced onion and salt and pepper to taste. Stir to combine. Reduce heat to low and let mixture heat thoroughly for 5 minutes.
Preheat grill to medium heat.
Sprinkle some cheddar cheese down the center of each tortilla. Add a few heaping tablespoons of the beef mixture on top of cheese. Drizzle a little mustard on top of the beef, and then add diced tomatoes.
Roll up each tortilla burrito-style.
Place wraps on a preheated grill and grill for 3-5 minutes, or until cheese is melted. Carefully remove wraps from grill and place on a plate. Gently unravel wrap to add some lettuce. Re-roll wrap and then cut in center diagonally.
Serve immediately.