Preheat the oven to 350F.
Remove flesh from sweet potato, discard skin and mash in a large bowl.
Add turkey, egg, dried onion, 1/4 cup ketchup, marjoram and 1 teaspoon kosher salt, and mix with the ground turkey using a fork until mixed well.
In a small bowl combine 2 tablespoons of the ketchup with Worcestershire sauce.
Shape into a loaf and place on a baking sheet. Spoon sauce on top.
Bake uncovered for 55 minutes, remove from oven and let it sit for 5 minutes before slicing. I topped with fresh chives.