Preheat the oven to 350 degrees F.
Place the sweet potatoes
into a large bowl.
In a wok
or saute pan, toast the cumin and Sichuan peppercorns for 1 to 2 minutes until fragrant. Transfer to mortar and pestle
or spice grinder
Sprinkle the spices
and salt over the sweet potatoes, drizzle
with oil and toss to coat. Transfer to a baking sheet and roast
until tender, 30 minutes.