Preheat oven to 400 degrees F.

In a large bowl, combine ground turkey, chopped onion, chopped spinach, chopped parsley, bread crumbs, dijon mustard, egg white, salt, and pepper.

Mix all ingredients thoroughly until well combined.

Transfer the meatloaf mixture to a baking sheet.

Shape the mixture into a 10-inch loaf.

Spread ketchup evenly over the top of the meatloaf.

Bake in the preheated oven for 45-50 minutes, or until cooked through and no longer pink inside.

Let the meatloaf rest for a few minutes before slicing.

Serve warm, topped with marinara sauce if desired.