Combine shrimp, tempura powder and cold water in a large mixing bowl. Give it a good mix with your hand, until shrimp is coated evenly with batter.
Heat enough oil in a medium size pot to fry shrimp, around 350°F to 365°F. To check temperature, drop a dollop of batter to hot oil. If batter starts bubble and float to surface of oil in 3 to 4 seconds, it’s ready! Drop shrimp one by one, make sure they are not stick to each others. Fry shrimp 2 to 3 minutes or until shrimp is fully cooked and golden brown crispy outside. Do batches to not crowd pot. Remove from oil and place on a paper towel lined plate.
Combine all ingredients for sauce in a mixing bowl and mix well.
Toss fried shrimp in sauce until evenly coated. Transfer to a serving plate and enjoy immediately!