Peel and cube sweet potatoes. Add to a large bowl and cover with cold water. Soak at room temperature for 30 minutes. Drain and rinse to remove excess starch, then pat dry with a clean towel.
In a small bowl, stir together cornstarch, salt, garlic powder, onion powder, pepper, and dried herbs.
Transfer potatoes to a large mixing bowl. Toss in oil, then toss in the dry spice mixture until evenly coated. Transfer to a baking sheet lined with parchment paper.
Roast potatoes for 40-45 minutes, stirring every 10 minutes to ensure even cooking. Remove from oven when potatoes are fork tender and browned on the exterior.