Make each omelette in seperate batches . Beat the egg with 1 tbsp water. Heat the oil in a medium non-stick pan. Add the egg and swirl round the base of the pan, as though you are making a pancake, and cook until set. There is no need to turn it.

Carefully tip the pancake onto a board, spread with the crushed avocado, sprinkle with the coriander and cheese if using, layer over the ham or turkey and top with tomatoes,  then roll it up. It can be eaten warm or cold .