Preheat oven to 180°C, gas 4.
Line 16 holes of a 24-hole muffin tin with paper cases.
Drain the kidney beans, rinse and drain again.
Beat together the softened butter and sugar until pale and creamy, then gradually add the eggs, beans, cocoa powder, baking powder, vanilla extract, salt and honey.
Mix well for another 4-5 minutes until the mixture is smooth. Divide between the paper cases and bake for 20-25 minutes until risen and springy to touch.
Leave to cool in the tin for 10 minutes then transfer to a wire rack to cool completely.
For the icing, halve and pit the avocados, scoop the flesh out of the skin with a spoon and roughly dice.
Mix in a blender with the cocoa powder, maple syrup, peanut butter, a pinch of salt and vanilla extract until smooth.
Spread the icing over the muffins and swirl with a spatula. Dust lightly with cocoa powder and serve.