Combine first 7 ingredients in a large bowl. Divide mixture into 6 equal portions, shaping each into a 1/2-inch-thick patty.
Place patties on a grill rack coated with cooking spray; grill 5 minutes. Turn patties over; grill 2 minutes. Divide cheese evenly over patties; grill an additional 5 minutes or until a thermometer registers 165°. Remove from grill; let stand 5 minutes.
Place onion slices on grill rack coated with cooking spray; grill 4 minutes on each side or until browned and tender.
Place rolls, cut sides down, on grill rack; grill 1 minute or until toasted. Place 1 patty on bottom half of each roll; top each serving with 1 onion slice, 1 tablespoon Chipotle-Poblano Ketchup, and top half of roll.