1In medium bowl, mash avocado with fork. Stir in tomato, horseradish and mayonnaise until well blended; set aside.
2Set oven control to broil. In both sides of beef, make cuts about 1/2 inch apart and 1/8 inch deep in diamond pattern. Sprinkle both sides of beef with grill seasoning. Place beef on broiler pan.
3Broil with top about 4 inches from heat 4 to 5 minutes on each side for medium-rare or until desired doneness. Transfer beef to cutting board; cover with foil and let stand 10 minutes.
4Thinly slice beef diagonally across grain. Divide beef evenly among roll bottoms. Top each with about 1/4 cup avocado mixture, 2 slices bacon and 2 tablespoons onions. Cover with roll tops.