Preheat your oven to 350 degrees F. Line two baking sheets with parchment paper and set them aside.

Place the raisins in a small bowl, cover with hot tap water, and let them soak for 5 minutes. Drain well and spread on a paper towel, patting them dry. Set aside. While those soak, grate the zucchini on the large holes of a box grater. Gather the shreds in a clean kitchen towel and squeeze firmly over the sink until no more water drips out. Measure 1 cup of the squeezed zucchini and set it aside.

In a medium bowl, whisk together the flour, oats, baking soda, cinnamon, nutmeg, and salt. Set this dry mixture aside.

In a large bowl, beat the softened butter, brown sugar, and granulated sugar together with a hand mixer on medium speed for about 2 minutes until light and fluffy. Add the egg and vanilla and beat for another 30 seconds until combined.

Add the dry ingredients to the butter mixture and stir with a wooden spoon or spatula until just combined, do not overmix. Fold in the squeezed zucchini and the dried raisins until evenly distributed throughout the dough.

Scoop rounded tablespoons of dough onto the prepared baking sheets, spacing them about 2 inches apart. Gently press each mound down slightly with your palm since these cookies do not spread much on their own.

Bake for 12 to 14 minutes, rotating the pans halfway through, until the edges look set and the tops are just barely golden. The centers may still look slightly underdone but they will firm up as they cool. Do not overbake or they will lose their chewiness.

Let the cookies rest on the baking sheet for 5 minutes before transferring to a wire rack to cool completely. They are good warm but the texture is best after 15 minutes of cooling.