GLAZED Mushrooms: Melt butter in ovenproof saute pan on medium heat. Add mushrooms; saute 5 min. or until browned. Add steak sauce and pepper; toss to evenly coat mushrooms.
BAKE in 300ºF convection oven 15 min., tossing every 5 min. Remove from oven; set aside.
FOR each serving: Grill 1 steak until desired doneness. Place 1/2 cup onion straws on one side of plate; top with steak and 1/2 cup mushrooms. Arrange 5 potato slices on other side of plate.