1.Heat oil in 24cm frying pan; cook onion, chilli, garlic and prawns, stirring, until prawns change colour. Remove from heat; stir in sweet chilli sauce, half the fish sauce, sprouts and coriander. Transfer to medium bowl; cover to keep warm. Wipe out pan.
2.In a medium bowl, lightly whisk eggs, the water and remaining fish sauce until combined. Heat 2 tsp of the extra oil in same pan; add a quarter of the egg mixture. Tilt pan to cover base with egg mixture. Push egg mixture from one side with a spatula and let uncooked egg run over base. Repeat; cook until egg is almost set. Top half the omelette with a quarter of the prawn mixture, fold omelette to enclose filling. Slide onto warmed serving plate.
3.Repeat with remaining oil, egg mixture and prawn mixture, wiping out pan after each omelette to make three more omelettes.
4.Cut lime into wedges. Trim and thinly slice extra onions. Serve omelettes with lime wedges, extra onion and coriander.
Instead of rolling the omelettes, top them with the filling and serve them open.Note