Break off the outside leaves of the lettuces. Lay them on a plate and season with salt. Leave for about 15 mins to 'bleed' and soften. Heat a large frying pan or wok until very hot. Toss the leaves with the olive oil and stir-fry for just a min until they begin to wilt. Mix in the rice wine vinegar and drain on paper towel. Tastes better than spinach!