In a large skillet, cook the bacon over medium low heat until crisp. Remove to drain on paper towels, then crumble. Drain away all but about 2 tablespoons of the bacon grease, then return the pan to medium heat. Add the onions and cook, stirring occasionally, about 5 minutes or until translucent.
Add the mushrooms and cook, stirring occasionally, for 5 minutes or until the mushrooms are golden brown. Add the garlic and cook for 1 minute. Stir in the undiluted mushroom soup and add the crumbled bacon back. Stir to combine.