Add banana, eggs, oats, protein powder, baking powder, cinnamon, vanilla, salt, and 1/4 cup milk to a blender.
Blend until smooth and pourable. If too thick, add a splash more milk. Aim for a thick but spoonable batter.
Heat a nonstick skillet or griddle over medium heat.
Lightly grease with butter or oil.
Pour 1/4 cup batter per pancake. Cook until bubbles form on top and edges look set, about 2–3 minutes.
Flip gently and cook 1–2 minutes more, until golden and cooked through.
Repeat with remaining batter, greasing the pan as needed. Serve warm with your favorite toppings.