Preheat oven to 400˚
Spray muffin tin with non-stick cooking spray, or line with muffin liners.
Combine mashed bananas, sugar, egg, oil, and milk in bowl or mixer, mix until combined.
Add gluten-free flour, baking powder, and salt.
Mix all ingredients until well combined, scraping down sides of the bowl as needed.
Pour batter into prepared muffin tins, about 3/4 full.
Optional: Sprinkle with cinnamon sugar.
Bake for 20 minutes, until tops are set and golden.
Cool in muffin pan for 5 minutes, transfer to cooling rack to cool completely.