Instructions

• Preheat the oven to 350°F (175°C). Line a baking sheet with parchment paper or a silicone mat, or lightly grease the sheet.
• In a medium bowl, whisk together 1 cup old-fashioned rolled oats, 3/4 cup quick-cooking instant oats, 3/4 cup all-purpose flour, 1/2 teaspoon baking soda, 1/4 teaspoon salt, 1/4 teaspoon cinnamon, and 1/8 teaspoon freshly grated nutmeg until evenly combined.
• In a large bowl, whisk 6 tablespoons melted unsalted butter and 1/2 cup loosely packed brown sugar until smooth.
• Whisk the wet additions into the butter–sugar mixture: 1 large egg yolk, 2 tablespoons milk, and 1 teaspoon vanilla extract until evenly mixed.
• Add the dry ingredients to the wet ingredients and stir with a spatula until just incorporated. The mixture may take a few minutes to come together; aim for a moist, scoopable dough rather than a wet batter. If the dough looks dry or crumbly, let it rest 5 minutes so the oats can absorb moisture — do not add ingredients beyond those listed.
• Fold in 1 cup freshly grated zucchini squash and 3/4 cup chocolate chips until distributed evenly through the dough.
• (Optional) If the dough is very soft and difficult to handle, cover and refrigerate for about 30 minutes to firm it up.
• Using a tablespoon or cookie scoop, drop rounded portions of dough onto the prepared baking sheet, spacing them about 2 inches apart.
• Bake in the preheated oven for 12 to 15 minutes, or until the tops and edges are lightly golden.
• Remove the baking sheet from the oven and let the cookies cool on the sheet for 5 minutes. Use a spatula to transfer cookies to a wire rack and cool completely before serving.