Preheat the oven to 350 F. Spray a non-stick muffin pan with cooking spray or line with paper liners.
Put bananas in a large bowl and mash with a fork. Add the eggs, butter and vanilla and mix until combined. Add the milk and mix until combined.
Add the oats, cinnamon, salt and baking powder to the banana mixture and mix to combine. Add 1/2 cup of chocolate chips and mix with a spoon until combined.
Divide the batter between 12 muffin cups. Sprinkle the remaining 1/2 cup of chocolate chips on top.
Put the muffin pan in the oven and bake for 40 minutes, or until the oatmeal cups are golden-brown and cooked through.