Preheat oven to 350˚ F. In small bowl, combine chili powder, onion powder, garlic powder and paprika; rub evenly over both sides of chicken breasts. Place chicken onto large sheet of foil; wrap tightly, crimping edges to seal. Place foil packet onto baking sheet; bake 8 to 10 minutes. Carefully open packet; bake 6 to 8 minutes more or until chicken is cooked through and juices run clear when pierced with fork. Set aside to cool. While chicken is cooling, line large bowl with lettuce; top with tomatoes, corn and onion slices. Shred cooled chicken with fork; add to lettuce mixture. Drizzle evenly with dressing.