Preheat oven to 350 degrees.
In a large bowl mix together bread and milk until it forms a paste.
On top of the paste, place the ground turkey, spinach, feta, red onion, Worcestershire sauce, salt, pepper, oregano, garlic, onion powder, and bread crumbs.
Carefully mix together until all of the ingredients are distributed throughout the meat.
Form meatball mixture into 18 - 20 meatballs and place on a baking sheet sprayed with cooking spray.
Bake for 20 minutes.
Place meatballs into the slow cooker with 3 cups of marinara sauce.
Cook on low for 4-5 hours.
Serve zucchini noodles.