Preheat the oven to 350°F (175°C) and line a 12-cup muffin tin with paper liners or grease it lightly.
In a large mixing bowl, whisk together the eggs, Greek yogurt, and olive oil until smooth.
Add the grated zucchini, grated carrot, chopped spinach, chopped red bell pepper, and shredded cheddar cheese to the wet mixture. Stir to combine.
In a separate bowl, whisk together the oat flour, protein powder, baking powder, baking soda, salt, black pepper, and garlic powder.
Gradually add the dry ingredients to the wet ingredients, folding gently until just combined. Do not overmix.
Divide the batter evenly among the 12 muffin cups, filling each about 3/4 full.
Bake for 22 to 25 minutes, or until a toothpick inserted into the center of a muffin comes out clean.
Remove the muffins from the oven and allow them to cool in the tin for 5 minutes before transferring to a wire rack to cool completely.