Preheat oven to 190ºC.

Mix the flour, baking soda, cinnamon, walnuts, and salt in a bowl.

In a seperate bowl beat the sugar and egg until you get a pale yellow mixture. Slowly add the oil while still mixing. Once the oil is mixed in add the mashed banana.

Add the dry ingredients to the wet ingredients and mix until incorporated.

Spoon the batter into prepared muffin cups. Bake for 18-20 minutes in the preheated oven.