Heat 2 tablespoons butter in skillet. Brown chicken for 5 minutes on each side, remove to plate. Complete in batches if necessary.
Heat remaining 2 tablespoons butter in skillet. Saute mushrooms about 10 minutes until browned. Add garlic and cook 1 more minute.
This chicken is great served alone with roasted vegetables on the side, or on top of zoodles, cauliflower rice, or brown rice.