Preheat oven to 350 degrees and line a muffin pan with paper muffin liners
Add tsp of vinegar to milk and allow to sit for 5 minutes
Add milk mixture to oats in a bowl and soak for 15-20 minutes
In the meantime, combine gluten free flour blend, xanthan gum, flaxseed meal, baking soda, baking powder, salt and cinnamon in a large bowl and whisk together well.
Add egg, brown sugar, vegetable oil and vanilla extract to oats and mix together.
Create a well in the dry ingredients and add the wet ingredients into it. Mix until just blended. Stir in raisins and nuts.
Use an ice cream scooper to fill each muffin liner.
Press sliced banana on top
Bake for 10 minutes, take out of oven, press banana into the muffin again and sprinkle with a little turbinado sugar ( you can avoid this step if you want to just put the banana in the middle of the muffin before baking it)
Continue to bake an additional 10 minutes or until a toothpick inserted into the center of the muffin comes out clean.
Enjoy warm out of the oven or cool
Recipe by Jackie Ourman at https://jackieourman.com/oatmeal-flax-muffins-gluten-free/