Preheat the oven to 350°F (180°C). Line an 8 x 8-inch baking pan with parchment paper, leaving an overhang for easy removal; set aside.

If not already done, shred the zucchini and place the shreds in a clean kitchen towel or several layers of paper towels. Squeeze out as much moisture as possible, then measure 1/4 cup of the squeezed shredded zucchini and set aside.

Peel and mash banana(s) until smooth to equal 1 1/4 cups mashed banana.

In a large mixing bowl, combine 2 cups rolled oats, 1/2 cup peanut butter, and the 1 1/4 cups mashed banana. Stir until evenly combined.

Measure 1/2 cup chocolate chips. Reserve about 2 tablespoons of the measured chips for the top (optional), then fold the remaining chocolate chips and the 1/4 cup squeezed shredded zucchini into the oat mixture until evenly distributed.

Transfer the batter to the prepared pan and spread it evenly with a rubber spatula. Sprinkle the reserved chocolate chips over the top, if using.

Bake in the preheated oven for 18–20 minutes, or until a toothpick inserted in the center comes out clean or with only a few moist crumbs.

Remove from the oven and let the bars cool completely in the pan on a wire rack. Use the parchment overhang to lift the slab from the pan, then slice into 8 bars.