Toss fish pieces with 2 tablespoons cornstarch in medium bowl to coat. Mix flour, 3 tablespoons oil, baking powder and 1/2 teaspoon salt in small bowl. Gradually add water, whisking until batter is smooth. Pour batter over fish and stir to coat. Let stand 15 minutes.

Whisk remaining 1 tablespoon cornstarch, pineapple juice, sugar, vinegar, hot pepper sauce and 1/8 teaspoon salt in small bowl to blend. Heat remaining 1 tablespoon oil in heavy medium skillet over medium-high heat. Add ginger and lemon peel and stir-fry until fragrant, about 30 seconds. Add bell pepper and stir-fry just to heat through, about 30 seconds. Add pineapple juice mixture and cook until sauce is thick and clear, stirring constantly, about 1 minute.

Heat 4 cups oil in wok or deep medium saucepan to 375F. Add batter-coated fish pieces to oil in batches and fry until crisp and golden, about 4 minutes. Using slotted spoon, transfer fish to paper towel-lined dish and drain. Reheat oil if necessary between batches.

Arrange fish on platter. Reheat sauce briefly, spoon over fish and serve.