Preheat oven to 350°F. In a large bowl, mash bananas until mostly smooth.
Stir in milk, peanut butter, maple syrup, egg, melted coconut oil, and vanilla until well combined.
Add oats, baking powder, cinnamon, and salt. Stir until just combined — do not overmix.
Scoop batter into silicone muffin tins (no greasing needed!), filling each about 3/4 full. This makes approximately 12-16 muffins.
Bake for 30 minutes until tops are lightly golden. Allow to cool for 5 minutes before removing. Drizzle with melted peanut butter and serve.