In a large bowl, combine the ground beef, Bar-B-Q sauce, Stubb's Beef Marinade, liquid smoke (optional) and Stubb's Beef Spice Rub. Use your hands to mix well. Once combined, separate the mixture to make six patties. Make a slight indent with your thumb in middle of each patty to keep it from swelling while on the grill.
Prepare your grill for direct medium-heat cooking. Lightly oil the grates and place your burger on the grill, indent side up. Cook burgers for 12-14 minutes or until preferred doneness (160°F) turning once during cooking. While burgers are cooking, add the onion slices to the grill and cook until lightly charred and soft, turning once. Also toast the buns.
To serve, top burgers with Bar-B-Q sauce, bacon, grilled onion and shredded cheese. Add additional toppings to your liking.