Cut 8 (1/2-inch-thick) slices from center of each sweet potato; reserve ends for another use, or discard. In large bowl, toss sweet potato slices, 1 tablespoon of the olive oil, 1/4 teaspoon of the salt and the pepper. Place slices in pan. Bake 18 to 20 minutes or until tender when pierced with paring knife. Turn slices over. Brush sweet potato slices with mustard.