Pat the thawed shrimp dry with a paper towel and set aside.
In a medium-sized bowl, whisk together the mayonnaise, chili sauce, rice wine vinegar, and Sriracha sauce. Taste and adjust flavors - add a pinch of salt if needed and add more chili sauce if you want it sweeter, add more rice wine vinegar if it is too sweet. (Read more about how to balance a sauce here.) Set aside the sauce.
In a shallow dish, whisk the egg whites until frothy. Put the flour and the panko breadcrumbs in two other shallow dishes.
Working in batches, dip the shrimp in the flour, making sure that both sides are well coated. Transfer the shrimp to the egg whites, and then finally coat the shrimp in the panko.
Heat the vegetable oil in a large skillet until smoking. Add the shrimp, cooking for 3 minutes on each side. Transfer to a paper towel lined plate.
Toss the shrimp, carefully, in the prepared sauce. Serve in lettuce and topped with green onions.