Heat oil in a large nonstick frying pan and add the prawns in a single layer. Cook for about 45 seconds each side, or until light golden. Add the sesame oil, garlic, ginger and chilli flakes and cook, stirring for about 30 seconds. or until the prawns are coated.
Add the water, sriracha, soy sauce and brown sugar. Continue to cook on medium high heat, stirring and turning the prawns, until the sauce has thickened and looks sticky, as in the photo.
Spoon some steamed rice onto two serving plates. Arrange a few steamed green beans on top, then the prawns. Garnish with the chilli, sesame seeds and spring onion.