Combine mayonnaise and 3 tablespoons barbeque sauce. Chill until ready to serve.
Gently shape ground beef into four five-inch burgers. Season burgers as desired with burger seasoning.
Grill burgers over direct high heat (450°-550°F) with the lid closed as much as possible, until the internal temperature reaches 160°F for medium, 8-10 minutes, turning once. During the last few minutes of cooking, brush with barbeque sauce, turning once. Top with cheese.
Spray onion slices with cooking spray and grill with burgers. Cook until onions are tender, turning once.
To serve, place burgers on hamburger buns. Top with grilled onions, bacon and barbeque mayonnaise.
If peppered bacon is not available, regular bacon may be used.
Slather on the Weber® Sweet & Thick Original BBQ Sauce for deliciously saucy burgers.