Heat a little oil in a large skillet or pan, if desired. Add the chopped bacon and cook until it has rendered its fat and is crisp. Transfer to another plate.
Add 1 tablespoon of butter to the remaining bacon fat in the skillet. Quickly saute the garlic and onions in the butter and bacon fat just until the onions have changed color.
Add the mushrooms and asparagus, give a quick stir then cover and cook on low until the asparagus is crisp-tender about 5 minutes depending on how thick your asparagus spears are.