Preheat your oven to 400°F. Pierce the sweet potatoes with a fork and bake for 45-60 minutes until tender.
In a medium saucepan, combine cranberries, diced apple, brown sugar, cinnamon, nutmeg, and salt. Cook over medium heat for 10 minutes until cranberries burst.
After baking, let sweet potatoes cool for 10 minutes, then scoop out the flesh into a mixing bowl, leaving a border in the skin.
Mix the sweet potato flesh with the cranberry-apple mixture and Greek yogurt. Spoon the filling back into the sweet potato skins and drizzle with maple syrup if using.
Return the stuffed sweet potatoes to the oven and bake for an additional 15-20 minutes until heated through.