Cut chicken into 1-inch-square pieces. In a mixing bowl, combine cornstarch, soy sauce, hoisin sauce, sugar, cilantro, ginger and garlic. Add chicken and toss to coat. Refrigerate, covered, at least 30 minutes.
Heat oven to 400°F. Fold each piece of foil in half twice to make a 6-inch square. Place a spoonful of chicken in the center of each piece of foil, dividing it equally. Fold foil squares on the diagonal; fold edges to seal. Place on a nonstick baking sheet and bake 20 minutes, or until chicken is no longer pink in the center.
