In a small mixing bowl, whisk together the mayonnaise, Thai sweet chili sauce, Sriracha, and rice vinegar until smooth; set sauce aside.
Ensure shrimp are completely dry by patting with paper towels.
Toss the shrimp in cornstarch until evenly coated, shaking off any excess.
Heat approximately 2 inches of vegetable oil in a heavy-bottomed pot or deep fryer to 375 degrees Fahrenheit.
Fry shrimp in small batches for 2 to 3 minutes until golden brown and cooked through.
Drain fried shrimp on a wire rack to maintain crispness.
Transfer hot shrimp to a large bowl and toss gently with the prepared sauce until thoroughly coated.
Serve immediately over a bed of shredded lettuce and garnish with sliced green onions.