Preheat the oven to 180 C | 350 F. Line a muffin pan with paper liners.
In a mixing bowl, add almond meal, flax, flaxseed meal, cacao powder, baking soda and salt and whisk well.
In a large mixing bowl, beat the egg and add mashed banana, maple syrup, oil, vinegar and milk. Mix until smooth and creamy.
Add the almond meal mixture and mix until just combine. Fold in the dark chocolate chunks, leaving few aside to sprinkle on top.
Scoop the muffins batter into the paper cups and sprinkle the remaining chocolate chunks.
Bake for 20-23 minutes or until toothpick comes out clean. Cool on a wire rack.