Preheat oven to 170°C/340°F. Grease two deep 20cm (8in) round cake pans; line bases and sides with baking paper.
Combine orange juice and seeds in a small bowl; stand for 15 minutes.
Meanwhile, combine coconut milk and vinegar in a medium bowl; stand for 5 minutes.
Blend Natvia in a high-speed blender until consistency of icing sugar.
Sift flour, soda, baking powder and powdered Natvia into a large bowl. Make a well in the centre, add seed mixture, coconut milk mixture and orange rind; whisk until just combined. Divide mixture evenly between pans.
Bake cakes for 1½ hours or until a skewer inserted into the centre comes out clean. Cool cakes in tins for 30 minutes before turning out onto wire racks to cool.
Split cakes in half; refrigerate cakes for 2 hours.
Place one base layer of cake on a plate. Top with a quarter each of the yoghurt, blueberries and lemon rind. Repeat layering with remaining cake layers, yoghurt, blueberries and rind, finishing with the final cake layer, topped with yoghurt.
Blend extra Natvia in a high-speed blender until consistency of icing sugar.
Sift extra powdered Natvia into a medium bowl; stir in juice until smooth. Drizzle over top of cake. Top with edible flowers, if you like.
Cakes can be made to the end of step 6 a day ahead; store in an airtight container at room temperature. They can also be frozen for up to 3 months. Thaw, then continue with recipe. Serve cake topped with seasonal fruit, thin strips of citrus rind and edible flowers or unsprayed flowers to decorate. This cake is moist in the centre, however will firm up when refrigerated.