To prepare the batter, combine the flour with baking powder, sugar, and lemon zest. Add the kefir, oil, and eggs, then mix to form a smooth batter. Pour it onto a baking sheet that has been previously greased with oil and floured. Generously sprinkle the batter with fresh fruit. Raspberries were used in this instance, but various seasonal fruits may be substituted. Sprinkle the crumble topping over the fruit; prepare it by mixing flour, sugar, and butter. Bake at 180°C for approximately 30-40 minutes.