Add the bananas to a medium bowl. Mash with a fork.
Add the rest of the ingredients to the bowl. Gently combine with a spatula.
Place batter in the fridge or freezer while the oven preheats to 375 degrees F. (Chilling the batter helps it hold together for scooping and portioning.)
Line a baking sheet with parchment paper. Scoop and drop 1-tablespoon-size balls of the batter onto the prepared baking sheet. Press slightly to flatten to about ½-inch thick.
Bake for 12-14 minutes, or until cookies are lightly golden brown around the edges and firm to the touch.
Remove from oven and let cool on the baking sheet.
Notes
Store in an airtight container for up to 5 days in the fridge or at room temperature. Alternatively, let cool to room temperature, then freeze for up to 3 months in a freezer bag.
Be sure to use very ripe bananas with a lot of brown spots for the best flavor.
Substitute 1/4 cup peanut butter for the egg OR 2 tablespoons chia seeds and 2 tablespoons milk.
Gluten-free: Use certified gluten-free rolled oats.
Top with a drizzle of vanilla yogurt or melted chocolate chips.