Peel and dice the apples. Mix well with oat flakes, milk, sugar, salt, egg yolk, raisins, cinnamon, lemon zest and lemon juice. Beat the egg whites until stiff and fold into the mixture. Put in a greased baking dish sprinkled with breadcrumbs. Bake in a preheated oven at 190 ° C for about 45 minutes. Serve hot, with vanilla sauce or whipped cream, if you like.