In a medium mixing bowl, add your peeled and deveined large prawns, ensuring they are clean and dry. Sprinkle cornstarch evenly over the prawns, tossing gently to coat them completely. Allow them to rest while you prepare the next steps.

In a large wok or deep frying pan, pour enough oil to cover the base at least 1 inch deep and heat it over medium-high heat. You'll know it's ready when the oil shimmers and a drop of cornstarch sizzles upon contact.

Carefully add the prawns in small batches to the hot oil, ensuring they have enough space to fry evenly. Cook for about 2 to 3 minutes on one side or until they turn golden brown and crispy. Flip them over and fry for an additional 2 minutes. Using a slotted spoon, remove them and drain on paper towels.

While the prawns are frying, gather a bowl and combine sea salt, freshly ground black pepper, chili flakes, and garlic powder. Mix thoroughly until evenly blended.

Once your prawns are beautifully golden and drained, add them to the bowl with the seasoning mix while they are still warm. Gently toss to coat the prawns evenly with the mixture. Serve immediately on a platter, garnished with finely chopped green onions.