One day before, marinade the chicken according to the recipe directions. Grill the chicken and set aside any leftovers.
Whisk together the lemon juice, Thai fish sauce, and brown sugar.
Pile lettuce, onions, and basil in two salad bowls. Slice the leftover chicken on the diagonal and place strips on salad, then lay on mango slices. Drizzle on the dressing and sprinkle on the sesame seeds.