01 - Preheat oven to 350°F. Line a 12-cup muffin tin with paper liners or lightly grease with nonstick spray.
02 - In a large bowl, whisk together oat flour, protein powder, baking powder, baking soda, salt, and ground cinnamon until evenly blended.
03 - In a separate bowl, whisk eggs, almond milk, Greek yogurt, maple syrup, melted coconut oil, and vanilla extract until the mixture is smooth.
04 - Pour wet mixture into dry ingredients and gently mix just until combined, taking care not to overmix to ensure a tender crumb.
05 - In a small bowl, combine brown sugar, ground cinnamon, and melted coconut oil until a thick swirl is formed.
06 - Spoon batter to fill each muffin cup halfway. Add a small spoonful of cinnamon swirl mixture, top with remaining batter, and gently swirl with a toothpick or knife.
07 - Bake for 16–18 minutes, or until a toothpick inserted in the center emerges clean.
08 - Allow muffins to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.
09 - For glaze, stir powdered sugar with enough milk to achieve a drizzling consistency, then drizzle over cooled muffins before serving.