FOR each serving: Season 1 steak with salt and pepper; grill to desired doneness. Remove from heat; let stand 2 min. Meanwhile, grill cut sides of 1 baguette until lightly toasted.
SAUTE 1/3 cup each onions, green peppers and red peppers in 1 tsp. oil in skillet on medium heat 5 min. or until caramelized.
PLACE baguette on plate. Cut steak into 1/4-inch-thick strips; place in baguette. Top with 2 Tbsp. steak sauce, onion mixture and 1/4 cup cheese. Place under salamander for 8 sec. to warm cheese.