Preheat the oven to 375 degrees F.
In a large mixing bowl, mash the bananas with a fork until there are only a few lumps. Add the vanilla and egg and whisk it together in the mixture is completely combined. Whisk in the oil and milk until combined and then add the sugars and honey.
With a spatula or wooden spoon, stir in the baking powder, flour, cocoa powder, salt, mini chocolate chips and walnuts. Mix until all of the ingredients are combined and it will look like a cake-like batter.
Line a muffin tin with 12 paper-lined muffin liners and fill each one about 3/4 full. Sprinkle with more mini chocolate chips and walnuts (optional).
Bake for 15-17 minutes, rotating once until the muffin tops look set. Remove from the oven and let cool for a few minutes. Serve warm or at room-temperature for breakfast or a sweet snack!