For the rice-banana casserole, first prepare the rice: Steam rice in water for 15 minutes, strain excess water. Then steam rice with milk and a pinch of salt over low heat until the milk has boiled away. Remove from heat and add sweetener. Mix in the yolks and lemon zest and pour the whole into a greased mold.
Mix peeled, sliced banana with lemon juice and cinnamon. Beat egg whites until stiff, add a little sweetener and beat again until stiff. Mix in banana slices and spread over rice.
Bake the rice-banana casserole in the preheated oven on the middle shelf at 200 °C for about 6 minutes.