Preheat oven to 400°F. Rinse sweet potatoes to remove any dirt. Using a sharp knife, carefully make a series of 1/4-inch wide slices about 2/3rds of the way through the potatoes (do not slice all the way through.)
Place potatoes on a microwave-safe plate and microwave on high (100% power) for 3 minutes. Brush the potatoes with oil. Transfer to a 2-quart rectangular baking dish.
Bake for 30 to 40 minutes or until potatoes can be easily pieces with the tines of a fork. Meanwhile, stir together the maple syrup, walnuts, raisins and cinnamon. Pour over potatoes as soon as they come out of the oven.