Combine all pickled onion ingredients except onion in bowl; mix well. Add onions. Cover; let stand at room temperature 1 hour.
Combine dressing ingredients in bowl; mix well. Remove 1/4 cup dressing mixture; refrigerate. Add slaw ingredients to remaining dressing mixture; mix well. Cover; refrigerate until serving time.
Heat gas grill on medium or charcoal grill until coals are ash white.
Combine butter, 1 teaspoon chili powder, 1/2 teaspoon cumin, 1/4 teaspoon salt and 1/4 teaspoon ground red pepper in bowl; mix well.
Rub chicken breasts with butter mixture. Place chicken onto grill; grill, turning occasionally, 18-20 minutes or until internal temperature reaches 165°F and juices run clear when pierced with fork.
Spread reserved dressing mixture evenly over cut-sides of each roll. Layer bottom half of each roll with chicken breast and slaw mixture. Lift desired amount of pickled onions from brine mixture; place over slaw mixture. Top each with remaining half of roll.
- Leave remaining pickled onions in brine. Cover; store refrigerated. Pickled onions are great for sandwich toppers, tacos or burgers.
- Agave nectar can be found in the baking aisle near the sugars.