1 medium sweet onion, halved lengthwise, thinly sliced
1 teaspoon sugar
1 medium (1 cup) red bell pepper, finely chopped
1/4 cup chopped fresh cilantro
2 tablespoons fresh lime juice
1/4 teaspoon salt
8 (3- to 4-ounce) boneless skinless chicken breasts
2 teaspoons grill seasoning for chicken
8 Kaiser rolls, split
8 leaf lettuce leaves
Melt 2 tablespoons butter in 10-inch skillet over medium heat; add onion and sugar. Continue cooking, stirring frequently, 5-6 minutes or until onion begins to brown. Continue cooking, stirring occasionally, 10-15 minutes or until onions are deep golden brown and tender. Remove from heat; stir in all remaining relish ingredients. Set aside.
Heat gas grill on medium or charcoal grill until coals are ash white.
Meanwhile, place each chicken breast between layers of plastic food wrap. Starting in center and working outward, pound gently with meat mallet or rolling pin to about 1/4-inch thickness. Sprinkle with grill seasoning.
Place chicken breasts onto grill. Grill, turning once, 8-10 minutes or until internal temperature of chicken reaches at least 165°F and juices run clear when pierced with a fork. Top each with cheese slice; continue grilling 1-2 minutes or until cheese is melted.
Meanwhile, spread softened butter onto cut-sides of rolls. Place onto grill, buttered-side down. Grill 1-2 minutes or until rolls are toasted. Place 1 lettuce leaf and 1 chicken breast onto each bottom half of Kaiser rolls; top each with about 2 tablespoons relish.
- Prepare relish up to 2 days ahead. Microwave 5-10 seconds to heat slightly prior to assembling sandwiches.
- To add color variety, prepare relish with a mixture of yellow, orange and red bell peppers.
- The grill seasoning for chicken includes garlic, salt, onion, pepper and parsley.