FIRE-ROASTED Red Pepper Sauce: Mix ingredients in saucepan; cook on medium heat 15 min., stirring occasionally.
SLIDERS: MELT butter in saute pan. Add pepper rings and onions; saute until tender. Cook meat patties until medium (160ºF) or desired doneness. Set aside.
FOR each 3-serving portion: Spread 1 Tbsp. Fire-Roasted Red Pepper Sauce onto bottom of each of 3 buns. Top each with 1 burger, 1 cheese slice and middle section of bun; spread with additional 1 Tbsp. pepper sauce. Cover each with second burger, 2 oz. cooked vegetables and top of bun. Secure with toothpicks.