Prep the oven and pan: Heat oven to 350°F (175°C).
Line a 12-cup muffin tin with liners or lightly grease each cup.
Grate and drain veggies: Grate the zucchini and carrot. Place grated zucchini in a clean towel and squeeze out excess moisture. You don’t need to completely dry it—just remove the watery juice.
Mix the wet ingredients: In a large bowl, whisk eggs, Greek yogurt, maple syrup, oil, and vanilla until smooth and creamy.
Combine dry ingredients: In a separate bowl, stir together flour, oats, protein powder, baking powder, baking soda, cinnamon, nutmeg, and salt.
Bring it together: Add dry ingredients to the wet bowl.
Stir gently with a spatula until a few dry streaks remain. Fold in the grated carrot and zucchini, plus any optional add-ins.
Portion the batter: Divide evenly among the muffin cups. They should be about 3/4 full.
Bake: Bake for 18–22 minutes, until the tops spring back and a toothpick comes out with a few moist crumbs.
Cool: Let muffins cool in the pan for 5 minutes, then transfer to a rack to cool completely.
This helps set the crumb and keeps liners from sticking.