Preheat the oven to 350˚F (176˚C). Wrap the thawed spinach in a paper towel and squeeze out the excess water (this step is very important; if the spinach is too water, the dip will be less creamy).
In a large bowl, mix together the spinach, garlic, artichoke hearts, vegan cream cheese, vegan sour cream, half of the vegan parmesan, half of the vegan mozzarella shreds, salt, and pepper until well combined.
Transfer the mixture to an 8x8 inch (20x20 cm) square baking dish and sprinkle the remaining vegan parmesan and vegan mozzarella shreds over the top.
Bake for 25 - 30 minutes, or until bubbling.
Broil on high for 5 minutes to brown the top slightly and serve warm!