Preheat oven to 190 degrees Celsius (375 degrees Fahrenheit) and lightly grease a 2-quart baking dish.

In a large mixing bowl, whisk together the softened cream cheese, Greek yogurt, minced garlic, onion powder, salt, and pepper until the texture is uniform.

Fold the shredded chicken and chopped spinach into the cream cheese mixture until the ingredients are thoroughly incorporated.

Transfer the mixture into the prepared baking dish and distribute evenly using a spatula.

Top the casserole with shredded mozzarella and grated Parmesan cheese.

Bake for 25 to 30 minutes, or until the cheese is golden brown and the internal temperature reaches 74 degrees Celsius (165 degrees Fahrenheit).

Remove from the oven and allow the casserole to rest for 5 minutes before portioning.