Peel shrimp. (If shrimp is frozen, do not thaw; peel under running cold water.) Make a shallow cut lengthwise down back of each shrimp; wash out sand vein. Cut shrimp lengthwise into halves; cut crosswise into halves.
Mix shrimp, green onions, flour, water, egg, cornstarch, salt, sugar. sesame oil and white pepper.
Heat vegetable oil (1-1/2 inches) in wok to 350 degrees. Remove crusts from bread; cut each slice into 4 squares. Place 1 or 2 pieces of shrimp with sauce on each bread square.
Fry 5 squares at a time until golden brown, turning frequently - about 2 minutes. Drain on paper towel.
Do-ahead instructions: Prepare Shrimp Toast; cover and refrigerate no longer than 24 hours. Just before serving, heat uncovered in 400 degree oven until hot for 12 - 15 minutes. Drain on paper towel.