Line 2 baking sheets with parchment paper or silicone baking mats. Preheat the oven to 350°F (175°C) so it’s ready when the dough is chilled.
In a medium bowl, whisk together the flour, rolled oats, cinnamon, nutmeg, baking soda, baking powder, and fine sea salt until well combined. Set aside.
1 1/2 cups all-purpose flour, 1 cup old-fashioned rolled oats, 1 teaspoon ground cinnamon, 1/4 teaspoon ground nutmeg, 1/2 teaspoon baking soda, 1/2 teaspoon baking powder, 1/2 teaspoon fine sea salt
In a large mixing bowl, using a hand mixer or stand mixer on medium speed, beat the softened butter, brown sugar, and granulated sugar for 2–3 minutes, until light and fluffy.
1/2 cup unsalted butter, 3/4 cup light brown sugar, 1/4 cup granulated sugar
Beat in the egg and vanilla extract until smooth, scraping down the sides of the bowl as needed. It may look slightly curdled, which is fine at this stage.
1 large egg, 2 teaspoons vanilla extract
Add the unsweetened applesauce and mix just until incorporated. The batter will look a bit looser, which helps keep the cookies moist.
1/4 cup unsweetened applesauce
Gently stir the shredded, lightly squeezed zucchini into the wet mixture with a spatula until evenly dispersed, being careful not to over-mix.
1 1/2 cups shredded zucchini
Add the dry ingredient mixture to the wet ingredients in two additions, stirring gently with a spatula or mixing on low speed just until no dry streaks of flour remain. Do not over-mix.
Fold in the chocolate chips and chopped walnuts or pecans (if using) until evenly distributed. The dough will be thick and a bit sticky.
1 cup semi-sweet chocolate chips, 1/2 cup chopped walnuts or pecans
Cover the bowl and refrigerate the dough for 20–30 minutes. Chilling helps the flavors develop and prevents the cookies from spreading too much.
Using a small cookie scoop or tablespoon, scoop about 1 1/2 tablespoons of dough per cookie onto the prepared baking sheets, spacing them about 2 inches apart. For thicker cookies, keep the scoops mounded rather than flattening them.
Bake the cookies at 350°F (175°C) for 11–13 minutes, or until the edges are set and the tops look just dry in the center. They will be soft and slightly puffy rather than deeply browned.
Let the cookies cool on the baking sheet for 5 minutes, then transfer them to a wire rack to cool completely. If desired, sprinkle a tiny pinch of flaky sea salt on top while they are still warm. Enjoy slightly warm for melty chocolate centers.
flaky sea salt