In a small bowl, whisk together the mayonnaise, sweet chili sauce, sriracha, and fresh lime juice until completely smooth and combined. The lime juice brightens the richness of the mayo and balances the heat beautifully. Set the sauce aside while you prepare the shrimp—this allows the flavors to meld slightly.

Place the shrimp in a shallow bowl and pour the buttermilk over them, stirring gently to coat all pieces evenly. While the shrimp soak for 10 minutes, combine the cornstarch, salt, garlic powder, and black pepper in a separate shallow dish or plate. Mix thoroughly with a fork to break up any clumps in the cornstarch—this ensures an even, crispy coating.

Heat the vegetable oil in a deep skillet or saucepan to 350°F (use a thermometer for accuracy). While the oil reaches temperature, working in batches, remove the shrimp from the buttermilk one at a time and dredge thoroughly in the cornstarch mixture from Step 2, shaking off excess. I like to double-coat mine by briefly dipping them back into the buttermilk and then the cornstarch again—this creates an extra-crispy exterior that really stands up to the sauce.

Carefully place the coated shrimp into the hot oil and fry for 1.5 minutes on the first side until golden and crispy. Flip each shrimp and fry for another 1.5 minutes on the second side. Work in batches to avoid overcrowding the pan, which drops the oil temperature and results in soggy coating. Transfer the cooked shrimp to a rack or paper towel-lined plate to drain.

While the shrimp are still warm, transfer them to a bowl and pour the sweet chili sauce from Step 1 over them. Toss gently to coat all pieces evenly, being careful not to break the crispy coating. Transfer to a serving plate and top with the thinly sliced green onions. Serve immediately while the shrimp are hot and the coating is at its crispiest.