[header] How to cook a sweet potato in the oven [title] Preheat the oven to 400 degrees fahrenheit (200 degrees celsius). [step] Line a baking sheet with nonstick aluminum foil. [substeps] If desired, you could coat the baking sheet with nonstick cooking spray or grease it with a little oil instead of using foil. 
[title] Pierce each sweet potato with a fork. [step] Use the prongs of a fork to pierce each sweet potato about 6 to 10 times, spacing the piercings apart in a relatively even manner.