Combine all sauce ingredients in a small saucepan, bring to a boil then turn to simmer. Continue to cook at high heat until sauce has thickened and reduced by half. Add a small splash of sesame oil and transfer to a squeezable sauce bottle or bowl and keep warm.
Combine eggs, salt and pepper in a bowl and beat with a fork. Set aside.
Slice broccoli florets as thin as possible. This will help them cook faster.
Using a sharp knife, slice prawns in half horizontally by placing the knife along the spine of the prawn and moving the knife directly across until you have two halves.
Using a non-stick frying pan, heat some oil and add broccoli. Cook over high heat until a little charred.
Add another small splash of oil to the pan and add mushrooms, cabbage, garlic, ginger and chilli. Cook for around 1 minute.
Place prawns into pan and season all the ingredients with a little salt and pepper. Pour over beaten eggs and gently swirl around the pan to coat everything evenly. Cook over medium heat so the bottom doesn’t burn. After 30 seconds scatter with bean sprouts and cover the pan with a lid so the top of the omelette sets.
When the omelette is cooked through, flip into a half-moon shape and transfer to a plate. Pour over Foo Young sauce and garnish with spring onions and extra bean sprouts.