Preheat your oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease with cooking spray.
Mash the bananas: In a large mixing bowl, mash the ripe bananas until mostly smooth with very few lumps remaining.
Mix the wet ingredients: Add the eggs, almond butter, maple syrup, vanilla extract, and almond milk to the mashed bananas. Whisk until smooth and fully combined.
Combine the dry ingredients: In a separate bowl, whisk together the oat flour, protein powder, baking powder, baking soda, cinnamon, and sea salt.
Make the batter: Gradually fold the dry ingredients into the wet mixture using a spatula. Mix gently until just combined. Do not overmix.
Add optional mix-ins: Fold in chocolate chips, nuts, chia seeds, or hemp seeds if desired.
Fill the muffin tin: Divide the batter evenly among the 12 muffin cups, filling each about three-quarters full.
Bake the muffins: Bake for 20–22 minutes, or until the tops are golden and a toothpick inserted into the center comes out clean.
Cool and serve: Let the muffins cool in the pan for 5 minutes before transferring to a wire rack. Serve warm or store for later.