Scrub sweet potatoes. Pressure cook sweet potatoes in the Ninja Foodie for 6 minutes. Release the pressure manually. Remove potatoes and lay on a platter to cool. When completely cooled, cut in half. Carefully scoop out the center leaving a 1/4 inch shell. Turn sweet potatoes with the shell side up. Brush lightly with butter. Sprinkle with garlic powder and season salt. Turn shells over and brus insides with butter and sprinkle with garlic powder and season salt. Lay 1/2 of the sweet potatoes in a single layer with the skin side up in the fryer basket. *Set Ninja Foodie to Air-fry following manufacturers instructions. Set timer for 10 minutes. After the sweet potatoes skins have roasted for 10 minutes, open Foodie and turn them. Set the timer for 10 minutes, close lid, and continue roasting the sweet potatoes skins. Turn off Foodie and remove the roasted sweet potatoes. Sprinkle with parmesan cheese. Repeat from * with the remaining sweet potato skins. Serves 4.