Preheat the oven to 325°F. Place paper liners in a muffin pan. Spray the liners lightly with cooking spray, and set aside.

In a large mixing bowl, whisk together the flour, baking powder, salt and pepper. Set aside.

In a separate medium bowl, combine the milk, yogurt, egg and oil until well mixed. Add the wet ingredients to the dry ingredients and whisk until just incorporated. Fold in the zucchini, cheddar, parmesan, green onion and thyme. Mix until combined. The batter will be very thick.

Using an ice cream scoop or a 1/3 cup measuring cup, fill the muffin cups about two-thirds full. Bake for 20 to 25 minutes, or until a toothpick inserted in the center comes out clean.

Allow the muffins to cool in the pan for at least 10 to 12 minutes before removing.

Store any leftover muffins in an airtight container at room temperature for up to 3 days.