In a bowl, soak the shrimp in buttermilk for 10 minutes.
In a separate bowl, mix flour, salt, and pepper.
In another bowl, place panko breadcrumbs.
Coat each shrimp in the flour mixture, shaking off excess.
Dip the floured shrimp in buttermilk again, then coat with panko breadcrumbs.
Heat oil in a deep skillet over medium-high heat.
Fry the shrimp in batches until golden brown, about 2-3 minutes per side.
Remove shrimp and place on paper towels to drain excess oil.
In a small bowl, mix mayonnaise, sweet chili sauce, and sriracha.
Toss the shrimp in the sauce and garnish with sliced green onions.