Preheat the oven to 350 degrees F. Spray a baking sheet with non-stick cooking spray. Set aside.
Add the drained spinach, bread crumbs, onion, Parmesan, butter, eggs, garlic, oregano, thyme, and basil to a large mixing bowl. Stir until evenly combined. Check the seasoning and add salt and pepper to taste.
Use a cookie scoop to portion the spinach mixture. Roll each scoop into a 1-inch ball and place them on the prepared baking sheet, leaving room between each ball. (There should be 20-22 balls.)
Bake for 20-25 minutes or until the balls start to turn lightly golden brown. Remove from the oven and serve warm or at room temperature with tzatziki sauce for dipping.