Preheat oven to 350°F (175°C). Spray a 12-cup muffin pan with nonstick spray or line with muffin cups. (To make mini muffins, use a mini muffin pan and liners.) Set the pan aside.

In a medium bowl, whisk together 1 3/4 cups whole wheat pastry flour, 1 teaspoon baking soda, and 1/2 teaspoon salt. Set the dry mixture aside.

In a large bowl, mash the 2 ripe bananas until mostly smooth. Add 1 cup shredded zucchini, 1/2 cup creamy peanut butter, 1/4 cup canola oil, 1 egg, 1 teaspoon vanilla, and 1/2 cup brown sugar. Whisk (or beat with a stand mixer) until the wet ingredients are combined.

Pour the dry ingredients into the wet ingredients and stir gently until just combined. Do not overmix.

Fold 1/4 cup chocolate chips into the batter.

Portion the batter into the prepared muffin cups: for regular muffins, fill each cup about halfway; for mini muffins, fill each cup about one-third full.

Using the 12 tablespoons heaping Nutella provided, add Nutella to each muffin as follows: - For regular (12) muffins: drop 1/2 tablespoon Nutella into the center of each partially filled cup, then spoon additional batter over the Nutella to fill each cup about 3/4 full. Add the remaining 1/2 tablespoon Nutella on top of each filled cup and gently swirl with a knife or toothpick. - For mini (24) muffins: drop about 3/4 teaspoon Nutella into each partially filled mini cup, then spoon additional batter over the Nutella to fill each cup about 3/4 full. Add about 3/4 teaspoon Nutella on top of each filled mini cup and gently swirl with a knife or toothpick.

Bake regular muffins 20–25 minutes (mini muffins 10–12 minutes), until the tops are lightly browned and a toothpick inserted into the muffin (avoiding the Nutella center) comes out with a few moist crumbs but not raw batter.

Let the muffins cool in the pan for 10 minutes. Loosen the edges with a knife if needed, then transfer the muffins to a cooling rack to cool further.