Put the cornflour in a bowl with the egg whites, pepper, salt and water. Mix to a smooth paste.
Pour the oil into a frying pan so you have a thin layer of oil covering the base of the pan. Dip the prawns in the batter and fry over a high heat for 3-4 minutes until crispy and golden on both sides. You will need to do this in a few batches. Drain on kitchen paper.
Now wipe out the pan and pour in another drizzle of oil. Add the cashews and toast until golden. Add the slices of garlic and cook till crisp and brown.
Add the onion and pepper chunks and cook till just soft but still crunchy – this should only take 3-4 minutes. Now add the pineapple, ketchup and vinegar and mix through.
Toss in the prawns and mix through, then finish by mixing in the coriander and spring onions. Serve with noodles.