Preheat your oven to 350°F (175°C) and line a muffin tin with paper liners or grease the cups.

In a large mixing bowl, combine mashed bananas, Greek yogurt, eggs, and peanut butter; blend until smooth.

Gradually add oats and cocoa powder, folding gently to combine without overmixing.

Fold in your choice of berries or additional mix-ins into the batter.

Scoop the muffin batter into prepared muffin tins, filling each cup about 3/4 full.

Bake for 18-20 minutes until golden brown and a toothpick comes out clean.

Let cool for about 5 minutes in the tin before transferring to a cooling rack.