Allow the spinach to thaw completely and then press it into a fine mesh sieve to remove as much water as you can.
In a large mixing bowl, use a hand mixer to the whip the goat cheese with ¼ cup of Greek yogurt until fluffy. Add the remaining cup of Greek yogurt and mix until well combined. Mix in the onion, garlic, spinach and seasonings. Finally, fold in the parmesan and half of the mozzarella.
Spread the mixture into an 8x8 inch baking dish (or similar size) and cover with the remaining half of the shredded cheese. Bake for 20-25 minutes at 375 °F until the cheese is melted and bubbly.
Serve hot with crackers, fresh vegetables, sourdough bread and more.
Notes
Make AheadThis dip can be fully assembled, covered with plastic wrap or a tight fitting lid and refrigerated up to 2 days in advance. When ready, bake as directed.LeftoversStore leftovers in an airtight container (or covered in the baking dish) in the refrigerator for up to 3 days.