Combine flour, oatmeal, pecans, chocolate, nutmeg, salt, baking soda, cinnamon, and baking powder in a bowl. Stir to incorporate, then set aside.
In a separate bowl, whisk egg and oil together until combined. Add sugar and continue to whisk until incorporated.
Whisk the vanilla extract into the mix, then add the mashed bananas to the batter.
Stir the dry ingredients into the wet ones until the ingredients are combined and a dough has formed.
Fill your greased or parchment-lined muffin cups with approximately 2 tablespoons of the banana oatmeal muffin batter.
Bake for 18-20 minutes at 375F.
Serve while warm, and enjoy :)
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Notes
When mixing your ingredients, sift your flour through a mesh sifter. This breaks up any lumps, making the flour lighter, airier, and easier to combine with the other ingredients. In turn, this also gives you light, fluffy muffins.
Feel free to customize your easy banana oatmeal muffin recipe by adding mix-ins like shredded coconut, dried fruits, or chia seeds. This can add texture and additional flavors.