Preheat the oven to 375 degrees F. Position a rack in the center of the oven and line a baking sheet with parchment paper.
In a small food processor or blender, pulse the sunflower seeds until ground into a fine flour. Transfer to a large mixing bowl and set aside.
Place the thawed spinach in a clean dish towel and squeeze the water out—the result should be a compact mound of spinach the size of a baseball. Add to the mixing bowl containing the sunflower seeds, along with the onions, basil, garlic, Parmesan or Manchego, eggs, butter or ghee, oregano, salt and pepper. Mix until full combined.
Using a melon-baller or tablespoon, portion the spinach batter into 1 1/2 inch balls and arrange them on the lined baking sheet. You should have about 20 to 24 total. Chill uncovered in the refrigerator for at least 30 minutes, and up to 4 hours.
Meanwhile, make the yogurt sauce: combine all the ingredients in a bowl and whisk until smooth. taste for seasoning and set aside.
Bake the spinach balls in the oven for 15 minutes, or until a light brown crust has formed on the bottom. Remove the tray and turn the balls to rest on another side. Return to the oven for another 15 minutes, or until crispy all around and browned on the second side.
Serve the balls warm or room temperature, alongside the turmeric yogurt for dipping.