Add the mashed bananas to a medium bowl. Add the rest of the ingredients, including the chocolate chips if using. Stir to combine thoroughly with a spoon.
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 1/2-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.
If you want to add icing, you can drizzle cookies with vanilla yogurt. Place yogurt into a zip-top bag with a small corner cut off and pipe over the cookies.
Serve immediately or store.
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. These cookies don't have any other added sugar, so it's crucial that the bananas are super sweet.
If you’d like to make these cookies a little sweeter, you can add 2 tablespoons brown sugar, honey, or maple syrup to the batter.
Substitute 1/4 cup peanut butter for the egg if desired.
To make a more uniform batter, you can use quick oats or briefly grind old-fashioned rolled oats in the food processor or blender to make quick oats.
Gluten-free: Use certified gluten-free rolled oats.
Egg-free: Omit the egg and add 2 tablespoons milk or additional banana.
Top with vanilla yogurt or melted chocolate chips.