Preheat oven to 350°F and set an oven rack in the upper third of the oven. Spray an 8×11 baking dish with cooking spray, then set aside.

Set thawed frozen spinach over a colander and wring out any excess moisture with a clean kitchen towel or your hands.

In a large bowl, mix Greek yogurt and cream cheese until smooth. Add spinach, 1 cup mozzarella, Parmesan, garlic powder, onion powder, salt, and pepper. Mix until combined.

Transfer to prepared baking dish and smooth it out to an even layer. Top with remaining ¼ cup of mozzarella.

Bake until cheese is melted, about 5-10 minutes. Switch oven to a high broil and place dip on top rack. Broil until cheese is golden brown and bubbling, 2 minutes. Serve immediately with crackers, bread, or pita.