Directions

1. Coat grill rack with nonstick cooking spray. Preheat grill to medium-high (350°F to 400°F). In a large bowl combine beef, onion (if desired), Worcestershire and pepper. Shape into 4 patties about -inch thick.
2. Place patties on grill. Grill, covered, 4 to 6 minutes per side or to desired doneness. Place Brie on patties during the last 2 minutes of grilling.
3. Meanwhile, place a skillet or large sheet of heavy-duty foil directly on grill. Add oil and mushrooms; sauté until mushrooms are tender. Season with salt and pepper to taste. Remove mushrooms from grill; set aside.
4. Place burgers on buns, top with mushrooms and desired toppings, and serve.