Roast sunflower seeds in a pan without fat. Remove from the pan and set aside. Peel oranges and grapefruits so that the white skin is completely removed. Cut oranges into slices.
Fillet grapefruits. Rinse lime with hot water and rub dry. Finely grate the peel and squeeze the juice. Puree banana, lime juice and lime zest. Mix yoghurt and banana puree.
Arrange orange slices, grapefruit fillets, oat flakes and banana-coconut yoghurt in four bowls. Sprinkle with roasted sunflower seeds. Serve decorated as desired with lemon balm, lime zest and coconut chips.