For marinade, combine 1 Tbsp of the oil, the soy sauce, sherry and pepper in a small bowl. Place chicken in a shallow dish. Rub marinade over chicken. Coat lightly with cornstarch. Refrigerate at least 30 minutes.
For lemon sauce, in a small saucepan over medium-high heat, combine sugar, ketchup, lemon juice, 1 tsp oil, salt, and 3/4 c water. Bring to a boil, stirring occaisionally. Add dissovled cornstarch and stir until slightly thickened. Keep warm.
In a wok or large frying pan, heat remaining oil. Add chicken stir-fry over medium-high heat until golden brown on each side, about 8 minutes. Remove with tongs and cut into 3/4" wide strips. Set aside and cover with foil to keep warm.
Add snow peas, bamboo shoots, and water chestnuts to work and stir-fry 2 minutes; transfer to heated serving plattter. Top with chicken and spoon lemon sauce over all.