Mix together the wheat flour, oat flakes, sugar and melted butter and spread or crumble half of it into an approx. 20 cm casserole dish.
Peel the bananas and place on the batter. Brush with lemon juice mixed with powdered sugar. Grate the chocolate, place on the bananas and spread the remaining batter on top as a crumble.
Bake at 200 ° C top / bottom heat for about 25 minutes.
Serve with vanilla ice cream.
Note: In Finland and Scandinavian countries it is common to measure the ingredients with the measuring cup. Hence the information in deciliters.