After grating zucchini, place in a colander over the bowl and gently squeeze to drain any excess water. Let sit and drain while preparing the dough.
In a large bowl, whisk the oats, flour, baking soda, and salt together. Set aside.
Using a hand mixer or a stand mixer fitted with the paddle attachment, cream butter, and sugars together until light and fluffy, about 2 minutes. Beat in the egg and mix until combined, about 1 minute, scraping down the sides and bottom of the bowl as needed. Add the maple syrup and vanilla and continue to mix until combined.
In 2 additions, add in the dry ingredients, scraping down the sides of the bowl in between additions.
On low speed, fold zucchini into the dough until incorporated. Fold in chocolate chips and pumpkin seeds as well.
Cover dough and chill in the fridge for at least 30 minutes or up to 4 days. If chilling for longer than a few hours, allow sitting at room temperature for at about 20 minutes before scooping and baking.
While the dough is chilling, preheat oven to 350°F (177°C) and line baking sheets.
Scoop dough in heaping Tbsps for each cookie, and place 2 inches apart on the baking sheets. Bake for 13-14 minutes or until lightly browned. For crispier edges, bake for 15 minutes. These cookies will not flatten too much, so if you want flatter cookies, press balls of dough down with fingers before baking.
Remove from the oven to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. Store at room temperature for up to 5 days or in the refrigerator for 1 week. Freezer friendly.