Mix together with a wire whisk the mayo, lime juice, chili sauce, vinegar, and fish sauce. Can be served at room temp or cold.
In a lidded container add shrimp, salt, garlic powder, ginger, and white pepper. Massage spice into shrimp to coat well. Whisk the buttermilk and lime juice (sriracha if you're using it) and pour over seasoned shrimp. Refrigerate covered for at least 1 hour.
Prepare breading bu tossing together cornstarch, panko, baking powder, salt, white pepper, and remaining garlic powder in a closed container and set aside.
To prepare, remove shrimp from the marinade shaking the excess off. Coat shrimp in the breading by sealing the container and shaking until fully breaded.
Heat oil to 375 in a skillet and fry in batches, being careful to not overcrowd the pan. Should cook for 4-5 minutes. They brown fairly quickly, so monitor the temperature. Drain on paper towels or wire rack.
Serve shrimp topped with chili sauce on lettuce with rice and desired garnishes.