Mix the oats, cocoa powder, whole wheat flour, brown sugar and baking soda together in a small bowl.
Pour in the vanilla extract and yoghurt and mix until all the liquid has been absorbed.
Scoop into a small ramekin and cook in the microwave on full power for 40 seconds for a gooey-all-over brownie, 50 seconds for a gooey-centred brownie or 60 seconds for a spongy brownie.