Preheat indoor or outdoor grill or oven broiler.
In a large skillet over medium-high heat, cook bacon until crisp; remove from skillet, drain on paper towels and keep warm.
Wipe bacon grease from skillet and add olive oil; sauté mushrooms and onions until mushroom liquid has evaporated and onions are translucent; remove from skillet and keep warm.
In a medium bowl, combine ground beef, salt, pepper and garlic; form into 4 patties. Grill/broil patties until they reach desired level of doneness.
Arrange salad greens on dinner plates; top each with a beef patty, half of a bacon slice and a portion of the mushrooms and onions.