Preheat oven to 350°F
Line an 8x8-inch baking pan with parchment paper or lightly grease it.
Grate zucchini and squeeze out excess moisture using a clean towel.
In a large bowl, whisk together applesauce, Greek yogurt, egg, vanilla, and honey. Stir in the grated zucchini.
In a separate bowl, whisk together oat flour, cocoa powder, collagen peptides, baking soda, salt, and cinnamon.
Gradually fold dry ingredients into the wet mixture until just combined. Stir in chocolate chips or nuts if using.
Pour the batter evenly into the prepared pan
Bake for 25–30 minutes or until a toothpick inserted in the center comes out with a few moist crumbs.
Let brownies cool completely before slicing for best texture.