Step 1Heat the grill or broiler to high.
Step 2Place the chicken on a plate and sprinkle with salt and pepper to taste. Spread the garlic over the chicken, sprinkle with the cayenne and drizzle with 1 tablespoon of the olive oil. Turn the chicken breasts over a few times to evenly coat with the seasonings.
Step 3Cut the tomato in half and squeeze out the seeds. Season the tomato, red onion, bell pepper and green onions with salt and pepper and brush with the remaining olive oil.
Step 4Place the vegetables cut side down on the grill. Turn them occasionally. The green onions will be done in about 5 minutes, the rest will take about 10 minutes. When the vegetables are charred, remove from the grill and set aside. Remove the skin from the tomato and pepper.
Step 5Meanwhile, grill the chicken breasts. Turn them over after 5 minutes, and cook until they are no longer pink inside, another 4 to 5 minutes. Remove to a serving plate.
Step 6Roughly chop the red onion, pepper, green onions and tomato. Mix together and spoon over the chicken breasts.