Combine beef steaks and 1/2 cup salsa in food-safe plastic bag; turn to coat. Close bag securely and marinate in refrigerator 6 hours or as long as overnight, turning occasionally.
Remove steaks from marinade; discard marinade. Place steaks in center of grid over medium, ash-covered coals. Arrange onion and pepper around steaks. Grill steaks, covered, 7 to 12 minutes (over medium heat on preheated gas grill, 8 to 12 minutes) for medium rare (145°F) to medium (160°F) doneness, turning occasionally. Grill onion and pepper 15 to 20 minutes (gas grill times remain the same) or until vegetables are tender, turning once.
Meanwhile, combine remaining 1/4 cup salsa, mayonnaise and chile powder in small bowl.
Remove and discard skins from peppers. Cut peppers into 1-inch thick slices; separate onion slices into rings. Carve steak into thin slices diagonally across the grain. Season with salt and pepper, as desired.
Spread beans on bottom half of each roll. Evenly layer beef, peppers and onions over beans. Spread salsa mixture on top half of each roll. Close sandwiches, pressing slightly together.