Take the prawns and using a knife, slice down the backs of the prawns to remove the vein. Depending on how daring your crowd is, you can either choose to cut off the legs and antennas or leave them on. Clean shrimp in cold water and drain water and then proceed to generously toss shrimp in cornstarch, covering entire shrimp.
Preheat a frying pan with oil to 375 degrees (high heat). Add in shrimp and let fry in the hot oil for ~2-3 minutes or until they are nice, golden and crispy. Remove and let shrimp drain on paper towel.
In a wok, add 2 table spoons of olive oil and bring to high heat and proceed to add chilies, garlic, white & green onions, salt, pepper, sugar, butter and fish sauce and bring to a high heat. Allow garlic, onions, and chili to cook for a 1-2 minutes and then add shrimp and stir-fry for another 1-2 minutes. Drain oil and serve.
Serve hot immediately on a bed of lettuce as an appetizer or as a main dish accompanied with white rice.
Optional dipping sauce: salt and pepper with lime juice in a small sauce plate.