Heat oven to 375°F. Wrap the thawed spinach in a clean kitchen towel and squeeze until very dry, then roughly chop. Drain the artichoke hearts and chop into bite-size pieces.
In a large bowl, stir the Greek yogurt, softened cream cheese, garlic, lemon juice, salt, and pepper until smooth.
Fold in the spinach, artichokes, 1/2 cup of the mozzarella, and the Parmesan until evenly combined.
Spread the mixture into a 1-quart baking dish and sprinkle the remaining 1/4 cup mozzarella over the top.
Bake 22-25 minutes, until bubbly and golden at the edges. For a browner top, broil 1-2 minutes, watching closely.
Let stand 5 minutes, then serve warm with vegetables, pita chips, or toasted baguette slices.
