Prep your pan and oven. Heat the oven to 350°F (175°C). Line a 12-cup muffin tin with paper liners or lightly grease it.
Mash the bananas. In a large bowl, mash the bananas until mostly smooth.
A few small lumps are fine.
Whisk in wet ingredients. Add eggs, Greek yogurt, maple syrup or honey, vanilla, and melted coconut oil or butter. Whisk until well combined and glossy.
Mix the dry ingredients separately. In another bowl, stir together oats, whole wheat flour, protein powder, baking powder, baking soda, cinnamon, and salt. Break up any clumps of protein powder with a fork.
Combine wet and dry. Add the dry mixture to the wet mixture.
Stir gently with a spatula until just combined. Do not overmix; the batter should be thick and slightly textured.
Fold in add-ins. If using nuts, chocolate chips, or flaxseed, fold them in now.
Fill the muffin cups. Divide the batter evenly among the 12 cups, filling each about 3/4 full. An ice cream scoop makes this easy.
Bake. Bake for 16–20 minutes, or until the tops are set and a toothpick inserted in the center comes out clean or with a few moist crumbs.
Cool. Let muffins cool in the pan for 5 minutes, then move to a wire rack to cool completely. This helps them set and prevents soggy bottoms.
Serve. Enjoy warm or at room temperature.
They’re great plain or with a smear of almond butter.