In a blender or food processor, combine the ginger, garlic, vinegar, peanut butter, red pepper flakes, and soy sauce. Process until well blended and chill. The sauce can be made and refrigerated up to 2 days in advance.
In a large saucepan, bring the water to the boil with the lemon slices and soy sauce. Drop in the shrimp, reduce the heat to a simmer, and cook 2 to 3 minutes, or until they turn pink. Drain, peel, and devein the shrimp. Chill them until ready to serve. The cooked shrimp can be refrigerated up to 2 to 3 days. To serve, arrange the shrimp on a platter with a bowl of the sauce and