Mix ingredients for marinade together. Coat chicken evenly with mixture and chill for 30 minutes.
To prepare batter, combine flour, cornstarch and baking powder. Mix well. Stir in oil and ice water. Refrigerate 30 minutes.
Heat oil for lemon sauce in a small saucepan over low heat. Add sliced lemons and saute for 40 seconds. Add chicken soup stock, lemon juice, and sugar. Simmer for 2 minutes. Mix together cornstarch and water and add slowly to lemon sauce, stirring constantly until thickened. Remove from heat and set aside.
Coat marinated chicken evenly with batter. Fry chicken in 1 1/2 inch-deep oil over medium-low hear. Do not overcrowd pan. If it appears that the chicken is browning before the inside is cooked, reduce heat. Cook until golden brown on outside and fully cooked inside (5-7 minutes).
Use remaining batter to coat zucchini and mushrooms. Deep fry in oil.
Slice chicken crosswise into 1-inch pieces and serve with zucchini, mushrooms and white rice. Reheat sauce and pour over sliced chicken.