Preheat oven to 375°F (190°C). Grease or line a 12-cup muffin tin.
In a large bowl, whisk together eggs, Greek yogurt, milk, and olive oil until smooth.
Stir in flour, baking powder, garlic powder, onion powder, salt, and pepper until just combined.
Fold in shredded chicken, chopped spinach, cheddar cheese, and Parmesan until evenly distributed.
Divide the mixture evenly among the muffin cups, filling each about 3/4 full.
Bake for 20–25 minutes, or until muffins are golden brown and a toothpick inserted in the center comes out clean.
Allow muffins to cool for 5 minutes in the pan before transferring to a wire rack to cool completely.
Serve warm or store in an airtight container for up to 3 days.