- Mix beef, garlic salt, onion, and pepper thoroughly in a bowl.
- Shape hamburger mixture into 6 patties, about ¾-inch thick.
- Mix bacon, cheese, mayonnaise, and mushrooms together and store in the refrigerator or cooler.
- Cook burgers on the grill, covered, for 5 or 7 minutes on each side.
- During the last 3 minutes, put ¼ cup cheese mixture on top of each burger.