Preheat: Heat oven to 350°F (175°C). Line an 8x8-inch pan with parchment (or grease well).
Prep produce: Drain and rinse black beans. Grate zucchini (lightly pat dry if very wet).
Blend: In a food processor or blender, puree black beans until mostly smooth. Add eggs, nonfat greek yogurt, cocoa powder, baking powder, vanilla, maple syrup, and whole wheat pastry flour; blend until smooth and no large bean bits remain.
Fold: Transfer to a bowl if needed. Fold in grated zucchini and chocolate chips.
Bake: Spread in the pan. Bake about 25-30 minutes at 350°F until edges are set and a toothpick has moist crumbs (not wet batter). Do not overbake.
Cool: Cool in pan before slicing.