Combine the chili sauce, lime juice, brown sugar, pepper flakes and 1/4 teaspoon salt; brush over steak. Broil steak 4-6 in. from the heat for 5-7 minutes on each side or until meat reaches desired doneness (for medium-rare, a thermometer should read 135°; medium, 140°; medium-well, 145°).
Meanwhile, in a large skillet, saute onion and green and yellow peppers in oil until tender. Add the garlic, pepper and remaining salt; cook 1 minute longer. In a small bowl, combine sour cream and horseradish. Slice steak and serve with pepper mixture and sauce.