Preheat oven to 375 degrees F and spray non-stick 12 muffin tin thoroughly with cooking spray. Muffins made with oats tend to stick to the pan, especially if using older or lower quality muffin pan. Make sure to use high quality non-stick 12 muffin tin sprayed well with cooking spray, foil lined paper cups or BPA free silicone cups. Set aside.In a large bowl, whisk together mashed bananas, peanut butter, milk, applesauce and vanilla extract. Add protein powder, oats, baking powder, baking soda, cinnamon and gently stir until combined. Batter will be quite thick. Fill each tin with batter dividing evenly, approximately 2/3 - full. Top each muffin with 1 tsp peanut butter and swirl with a toothpick. Bake for 20 minutes, remove from the oven and let cool in the tin for at least 45 minutes before transferring onto the cooling rack. The longer muffins cool, less crumbly they are. I find these muffins taste best a few hours after baking and cooled down.