Preheat oven to 350 degrees F. Line a 12-cup muffin pan with liners or grease liberally with olive oil.
Add olive oil (1/2 cup), honey (1/2 cup), eggs (2), and Greek yogurt (1/2 cup) to the bottom of a large mixing bowl. Whisk vigorously by hand or use an electric mixer to mix very well until completely smooth.
Add the vanilla (1 teaspoon), ground cinnamon (1 teaspoon), ground nutmeg (1/4 teaspoon), baking powder (1 teaspoon), baking soda (1 teaspoon), and kosher salt (1/2 teaspoon) to the bowl. Mix again until all ingredients are well incorporated.
Add the whole wheat flour (1.5 cups) to the bowl and mix using a wooden spoon just until there is no dry flour left.
Fold the grated zucchini (4 cups) and old fashioned oats (1 cup) into the mixture.
Bake at 350 degrees for 30-35 minutes, or until toothpick inserted in center of the muffins comes out clean.
For best results, allow to cool for at least 10 minutes before removing from pan.
These muffins can be kept for 1-2 days at room temperature in an airtight container or zip-top bag. For longer storage, I recommend freezing them. They're easily thawed in the microwave for only about 30 seconds.
The results of this recipe can vary depending on how dry or wet your zucchini is. Garden zucchini tends to be more watery than store-bought. I used store-bought for this- if your grated zucchini seems very wet, you can pat it gently with a clean towel before adding it to the batter (but don't dry it completely!). If your batter seems too wet, you can add a little more flour to it as well. And, you can always use one less cup of grated zucchini if you prefer.
The provided nutrition information does not include any added sodium from seasoning to taste, any optional ingredients, and it does not take brands into account. Feel free to calculate it yourself using this calculator or by adding the recipe to Yummly.