Preheat the oven at 200C.
Melt the margarine.
Mix the self-raising flour, cocoa powder, baking powder, salt, and baking soda.
In a different bowl, mix the agave syrup, vanilla extract, sunflower oil, margarine, yoghurt, milk and eggs.
Stir the dry ingredients together with the wet ingredients.
Cut the chocolate in small pieces, and stir it in the mixture.
Fill 2/3 of the muffin cups with the mixture (divide it over 10 muffin cups).
Bake for 20 minutes.