This one is great all year around.
You put yoghurt, a ripe banana, a cup of blueberries, and a cup of strawberries into your blender, and just blend for about a minute and a half. If you let it sit for a few minutes, it becomes thicker and thus fills you up nicely. You can add honey to sweeten it, although I think a ripe banana is enough, and add coconut flakes on top.
In summer, you can use frozen blueberries and/or strawberriess to make the smoothie cooler, or you can add an ice cube or two.
Perhaps you can put a bit of the smoothie into plastic ice-cream cone moulds and freeze them. It makes one healthy and tasty frozen yoghurt / ice cream the next day. Enjoy!