In A Small Skillet, Cook Sausage Over Medium Heat For 5-6 Minutes Or Until No Longer Pink; Drain. Remove Stems From Mushrooms And Finely Chop; Set Caps Aside. In A Large Skillet, Saute The Stems, Onions And Garlic In Butter For 4-5 Minutes Or Until Crisp-Tender. Stir In The Sausage, Bread Crumbs And 1/2 Cup Cheese. Spoon About 2 Tablespoons Into Each Mushroom Cap. Place On A Foil-Lined Baking Sheet; Sprinkle With Remaining Cheese. Bake At 350