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 bacon, bison, garlic, dijon 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 mayonnaise, tomatoes, and avocado slices. Finish off with another lettuce leaf on the top of each burger, and serve!