Preheat the oven to 400 ºF.
Cut the leeks into 0.5 cm (¼″) slices and lightly fry in a deep frying pan with extra-virgin olive oil until they start to turn golden brown.
Beat the eggs whites to stiff peaks. In a separate bowl, beat the two eggs and then add the beaten egg whites, almond drink, half the grated cheese, the golden-brown leeks and the flour. If you find there is too much mixture, you can pour off some of the almond drink; the exact proportions will vary depending on the size of the leeks. Add salt, pepper and oregano.
Pour the mixture into a pan covered with parchment paper, sprinkle the rest of the grated cheese on top and bake for 30 minutes.