Heat some cooking oil in a large frying pan or a wok over a high heat. Add the prawns and cook for about 90 seconds, until they are pink all over.
Remove the prawns from the pan and set aside. Turn the heat down to a medium, then add in the sliced onion and pepper and stir fry for a couple of minutes.
Chuck in the garlic and ginger and stir fry for a further minute.
Pour in 80ml of water, then add the soy sauce, sriracha, and soft brown sugar. Cook until the sauce starts to thicken.
Add the prawns back into the pan and add in the spring onions (hold some back for garnish). Stir well and warm through the prawns.
Serve with rice or noodles, then sprinkle over sliced spring onions and toasted sesame seeds.