Preheat oven to 380F - Prepare two ramekins (grease the bottoms and the sides with oil and slightly dust with flour).

In a medium bowl, add flour, salt, cinnamon, baking powder and baking soda and mix well. Add the walnuts and chocolate chips and set aside.

In another bowl, mash the banana with the sugar. Add the oil, yoghurt, vanilla extract and apple cider vinegar and mix until well combined.

Add the wet ingredients to the dry and mix just until combined (don't overmix).

Divide the batter into the two prepared ramekins, add more walnuts and slices of banana on top of it (optional) and bake for about 25 - 30 mins.

Cool the muffins for 5 minutes in the ramekins before flipping them out onto a cooling rack.