Arrange 2 racks in the oven, about 6 inches above the bottom, and 6 inches from the top heat source. Preheat oven to 425º F.
Line 2 large baking sheets with parchment paper and set aside.
In a small bowl, combine the arrowroot with the spices.
Add half of the sliced sweet potatoes to a large baking tray lined with parchment. Drizzle the fries with avocado oil (or olive oil), and use hands to rub the oil evenly into the potatoes.
Sprinkle the sweet potatoes with the spice mixture, then use hands to rub the spice mixture into the oil, evenly coating the potatoes.
Arrange the sweet potatoes on the baking tray, leaving space in between each. Allowing space around the potatoes is what crisps them up. If the sweet potatoes are crowded, they will steam instead of dry out and crisp up around the edges. Repeat with the remaining sweet potato fries on a 2nd baking sheet.
Add the two baking trays to the oven, one on the top rack and one on the bottom rack. Bake the sweet potato fries for 22 minutes.
Use a large spatula to flip the fries over, and then quickly spread them out to give the fries space to continue crisping. Bake for another 10-14 minutes, until the fries having begun to brown and look crisp on the ends.