Preheat the oven to 350°F (175°C). Line a dark metal baking sheet with parchment paper.
Mash the bananas, grate the apple and carrot, and chop the hazelnuts.
Combine all ingredients thoroughly in a medium-sized mixing bowl.
Using a ¼-cup measuring cup, drop scoops of dough onto the prepared baking sheet. You will end up with eight scoops. Flatten them slightly into a cookie shape with wet hands. They don't spread, so no worries if the cookies are close together on the sheet.
Place the baking sheet about ⅓ of the way from the top of the preheated oven. Bake for 15 minutes until the cookies are firm enough to hold together. Let the cookies cool before eating to give them more time to firm up.
The nutrition information is an estimate provided as a courtesy. It will differ depending on the specific brands and ingredients that you use. Calorie information on food labels may be wildly inaccurate, so please don't sweat the numbers too much.