Preheat oven to 375° F. Coat a 9 x 9” baking dish with non-stick cooking spray; set aside.
In a large bowl, place sweet potatoes, cranberries and apple slices. In a small bowl, combine brown sugar, nutmeg, cinnamon and salt. Sprinkle brown sugar mixture over sweet potato mixture and toss to combine. Pour sweet potatoes into prepared baking dish and add ¼ cup water; top with cubes of butter.
Cover tightly with aluminum foil and bake for 30 minutes. Remove from oven and stir to incorporate pan juices. Sprinkle granola over top and bake uncovered for 10 more minutes until granola is toasted and sweet potatoes are tender.