Whisk eggs, fish sauce and a generous grinding of black pepper. Heat 2 tbs vegetable oil in a wok and pour in egg mixture. Cook omelette for about 2 minutes or until brown and then flip over. Cook for 10 seconds and remove from heat. Slice into thin strips and set aside.
Heat another 2 tbs vegetable oil in the wok and stir fry garlic and onion until fragrant (about 20 seconds). Add prawns and stir fry for another 20 seconds. Add rice, fish sauce, soy sauce, sugar and another generous grinding of black pepper. Stir fry for another 20 seconds or until rice is evenly coated with sauce. Mix through omelette strips and coriander.
For the fish sauce with chilli, combine the two ingredients in a small serving bowl.
Serve fried rice alongside bowl of fish sauce with chilli, cucumber and wedges of lemon.