Heat a skillet over medium heat and cook the chopped bacon until cooked through. Use a slotted spoon to transfer the cooked bacon on to a paper towel. Save the bacon grease for another use. In a large bowl, combine beef, garlic, mustard, onion powder, dried oregano, salt and pepper. Mix together without overworking the meat. Divide meat into 4 equal parts an shape into patties, making a small indentation in the middle. Heat a grill to medium high heat. Place the burger patties on the grill, close the lid, and grill for 6 minutes. Flip the burgers, close the lid, and grill for 2 more minutes for medium rare, or longer if desired. Remove the burgers from the grill and let rest for 5 minutes. Place each burger on a lettuce leaf, then top with bbq sauce, tomatoes, and avocado slices. Finish off with another lettuce leaf on the top of each burger, and serve!