Heat a small (about 20cm) non-stick frying pan, add the bacon and cook over a medium-high heat for a few mins until cooked through. Remove the bacon from the pan with a slotted spoon and set aside. Once cool, cut into pieces.
Whisk the egg, flour and 4 tbsp water to make a batter, season and stir in the cabbage, half the spring onions, the prawns and the cooked bacon. Pour the oil into the pan, add the mixture and press down, then cook for 5 mins on a medium heat. Flip with a spatula, then cook for another 5 mins until golden and cooked through. Slide onto a plate and drizzle over the brown sauce and mayonnaise. Finally, scatter with the remaining spring onions.