Preheat your oven to 430 degrees Fahrenheit (220 degrees Celsius). Prepare a 12 count muffin pan by placing liners in each hole, or grease each hole with a little coconut oil.
Place a mesh sieve over a bowl. Place the whole wheat flour, baking soda nutmeg, cinnamon and salt in the sieve and push the ingredients through the sieve to break up any lumps.You will likely find that the wheat hearts will stay in the sieve. If so just tip these into the bowl of sifted flour then stir the ingredients with a whisk to make sure they are all evenly combined.
Add the yogurt, vanilla, egg, melted coconut oil, oatmeal, milk, mashed banana and sugar to a second bowl and mix together using your whisk. Using a whisk or a fork will help break up any lumps of sugar.
Pour the dry ingredients into the bowl of wet ingredients, add the walnuts (if using) and fold the batter together until everything is just combined.
Spoon the batter into your prepared muffin tin and place it in your pre heated oven.
Bake at 430 degrees Fahrenheit (220 degrees Celsius) for 5 minutes, then turn the temperature down to 350 degrees Fahrenheit (180 degrees Celsius) and bake for a further 15 minutes.
Once cooked through, remove the muffin tins from the oven and let them cool for 5 minutes. Then gently remove the muffins from the tin and place on a wire rack to cool completely.
Notes
Storage recommendations: Store these muffins in an airtight container to lock in their freshness. These banana oat muffins will keep for 1-2 days in your cupboard at room temperature or can be frozen for up to 3 months.