Preheat your oven to 350°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
Place the thawed spinach in a few layers of cheesecloth, a fine mesh nut milk bag or some paper towels, and squeeze until as much of the liquid as possible is removed. Set the dried, chopped spinach aside.
In a large bowl, place the butter and eggs, and whisk to combine well. Add the cheeses, oregano (pressing the dried herb in between your fingers to release the oils), parsley, bread crumbs, and dried spinach, and mix until just combined.
Add 2/3 of the tapioca starch, and incorporate into the mixture. The mixture should hold together easily when a portion is squeezed tightly in your palm. Add the remaining tablespoon of starch only if necessary for the mixture to hold together.
Roll the mixture into 1 1/2 inch balls between moistened palms, and place on the prepared baking sheet about 1 inch apart from one another.
Place in the center of the preheated oven and bake, for about 15 minutes or until the balls have begun to brown on the bottom & are cooked through, rotating once during baking. They will expand a bit during baking because of the eggs in the mixture. Serve warm.