Lightly mix the ground beef, salt, and pepper and form the mixture into four equal burger patties. Preheat the grill to 400 F. Toast buns on the grill for about 2 mins and set aside.
Brush grill with olive oil and char onions for about 6-8 mins and remove from grill.
Place burgers on the grill and cook for about 2-3 minutes on each side then top with the cheese to melt it.
Spread mustard and mayo on the bun, add the burger patty then top each burger with bacon slices, onion, tomato slices, and baby greens.