Peel and de-vein the shrimp leaving the tails intact.
Cut sirloin into two inch chunks.
Remove the seeds and stems from the bell peppers and cut into two inch pieces, cut the red onion the same.
Clean the mushrooms and trim off the bottom of the stem.
Take some kabob skewers and begin threading the shrimp onto the skewer alternating the shrimp with pieces of the onions, peppers and mushrooms.
Do the same thing with the sirloin and vegetables on separate skewers. (Keep the shrimp and beef on separate skewers as they have different cooking times, depending on how you like your beef cooked).
In a small sauce pan, melt the butter with the garlic until it simmers, remove from heat and whisk in the Worcestershire sauce. Set aside.
Prepare a gas or charcoal, charbroil grill and heat to medium high and brush grill grates with a little oil to keep the food from sticking.
Season kabobs with lemon pepper seasoning and place on the lightly oiled grill.
Cook the shrimp kabobs for about three to four minutes and brush with Worcestershire butter, flip and repeat. The shrimp are done when they have curled a bit, but are no longer translucent in the center.
Cook the beef kabobs until the desired temperature, brushing occasionally with the Worcestershire butter.
Place kabobs on a platter and drizzle with any remaining butter, serve hot.