Coat baking pan (half sheet tray) with one tbsp oil. In a large bowl, put cut sweet potatoes. Mix 3tbsp oil with spices and pour over sweet potatoes. Mix well with your hands making sure each piece is coated with spice mixture. Bake in top rack of heated oven for 25 minutes. Rotate pan in oven after first 10 minutes. Remove tray from oven after 25 minutes as the potatoes will be cooked.