Heat grill to medium heat. Combine dressing and chipotle peppers. Mix turkey, green peppers, garlic powder and 2 Tbsp. dressing mixture just until blended; shape into 4 (½-inch-thick) patties. Grill 6 to 7 min. on each side or until done (165°F), adding onions to the grill for the last 5 min. and grilling until charred, turning after 3 min. Place burgers on bottom halves of buns; top with remaining dressing mixture and onions. Cover with tops of buns. Special Extra: Grill burgers as directed. Top each with 1 KRAFT Singles; grill 1 min. or until melted. Continue as directed. Variation: Add 1 Tbsp. chopped fresh cilantro to dressing mixture before using as directed.