Preheat oven to 400°F.
Toss the tomatoes and onions with the chopped parsley, vinegar, about 2 tablespoons of EVOO, salt and pepper. Let stand while you prepare dinner.
Wring defrosted spinach dry in a clean kitchen towel. Place turkey in a bowl and make a well in the middle of it. Into the well, add the grated onion and garlic, egg, bread crumbs, grated Parmigiano, spinach, salt and pepper.
Form into 12 large balls and arrange on a nonstick cookie sheet. Drizzle the meatballs with EVOO, about 1/4 cup, and roast for about 20 minutes, or until cooked through.