Preheat oven to 350 degrees Fahrenheit. Spray 10 cavities in a muffin pan well with non-stick cooking spray and set aside.
To make the cream cheese filling:
Add the cream cheese, egg yolk, sugar, and vanilla to a small bowl. Beat with a hand mixer until smooth and set aside.
To make the muffins:
In a large bowl, whisk together the flour, baking powder, baking soda, salt, and cinnamon.
In a separate bowl, mix together the oil, granulated sugar, brown sugar, vanilla, egg, and shredded zucchini.
Add the wet ingredients to the dry ingredients and mix until just combined.
Scoop half of the batter into 10 of the muffin cavities, evenly distribute the cream cheese filling on top of the batter, then add the remaining half of the batter on top.
Bake at 350 degrees for 20-25 minutes or until a toothpick inserted into the center comes out clean.
Remove from the oven and allow to cool in the muffin pan for about 5 minutes. Remove the muffins from the muffin pan and transfer to a wire rack to finish cooling.
Notes
Muffins can be stored in an airtight container in the refrigerator for up to 5 days. These will freeze well for up to 2 months, thaw in the refrigerator overnight.