Finely chop 1 of the salad onions. Beat the eggs in a mixing bowl then stir in a splash of soy sauce and then the chopped onion. Season with pepper and a little salt and set aside.
Cut the remaining salad onions in half lengthways, then cut into long, thin strips. Heat 1 1/2 teaspoons of the oil in a small frying pan. Tip in the sliced salad onions and the chopped garlic and stir fry briefly until starting to colour. Toss in the prawns and bean sprouts and stir fry for a minute or two until heated through. Season with pepper, then set aside and keep warm.
Heat the remaining 1 1/2 teaspoons of oil in a 20cm diameter frying pan, and when hot, pour in the beaten eggs, bringing the mix in from the sides of the pan as its starting to set a little to create big, soft folds. Give a bit of a stir, leave to cook briefly, then stir again. When it looks brown underneath and softly set on top, tip the prawn and bean sprout mixture over half of the omelette and season with a few drops of extra soy sauce and sesame oil if you like. With the help of a spatula, fold the omelette in half over the filling, then slide it onto a warm serving plate and serve immediately.
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