Heat the oil in a non-stick skillet set over medium, medium-high heat. Sprinkle and rub chicken with chili powder, cumin, salt and pepper. Sear and cook the chicken 4 minutes per side, or until cooked through. Cool chicken, and then thinly slice.
Divide and mound butter lettuce on each of 4 plates. Arrange some chicken, mango, cucumber, bell pepper and cilantro (or mint) on each salad. Drizzle each salad with some of the dressing and serve.