Lightly brush grill rack with vegetable oil. Prepare the grill with medium hot coals, heat gas or heat broiler. Slice each lemon into 6 thin rounds. Pick out the seeds. Microwave the slices on a plate, covered, at full power for 1 minute. Season the chicken with lemon pepper and salt. Grill or broil the chicken until browned, about 4 minutes per side, an instant read thermometer should register 170ºF. Keep warm on a platter. Sprinkle the lemon slices with sugar, chili powder. Grill until browned, about 40 seconds per side. Place 2 slices on each breast to garnish, drizzle with any juice remaining in microwave dish.