In a small bowl combine the mayonnaise, chili garlic sauce, sriracha, vinegar and lemon juice. Cover and refrigerate until ready to use. The sauce can be made up to 4 days in advance.
Combine the beaten egg yolk with milk in a shallow bowl. Set aside. Combine flour, cornstarch and panko in another small, shallow bowl. Season with salt and pepper and set aside.
Working a few shrimp at a time, coat the shrimp in the egg mixture then toss in the breading.
Add oil to cast iron pan. Heat oil to 350ºF (180ºC). Fry shrimp, working a few at a time, cooking until golden brown on all sides, about 3 minutes.
Drain on a cooling rack or a paper towel-lined plate.
Once all the shrimp are fried, add to a large bowl. Spoon about ½ cup of the sauce over the shrimp and toss to coat them evenly.
For serving, arrange the shrimp on a bed of lettuce and garnish with the green onions. Serve immediately.