Chop the onion, garlic, and celery very finely (or use a food processor), then add to a large mixing bowl.
Add the turkey, egg whites, oats, and spices to the bowl and mix thoroughly. Make sure there are no pockets of spices or oats in the mix.
Chop the spinach, green peppers (stemmed and seeded), and parsley. The pieces should be about the size of a dime.
Add the vegetables to the bowl and mix everything until well-combined.
Line a baking sheet with parchment paper.
Roll the turkey mixture into 15 balls (about the size of golf balls) and place them on the baking sheet.
Bake for 25 minutes, until cooked through.
This recipe is for 5 servings. There are 3 meatballs per serving.I recommend using 93% or 85% lean ground turkey. 99% lean ground turkey doesn't have much flavor and tends to dry out while cooking.You are welcome to swap out herbs, spices, and vegetables in this recipe.Once cooked, meatballs can be stored in an airtight container in the refrigerator for 3-4 days. For longer storage, freeze individual servings in their own Ziploc bags. When you're ready to enjoy, you can take out a serving at a time to thaw.