Preheat oven to 400° F. Line Sheet Pan with Sheet Pan Liner.
Cut chicken into 2" pieces. Place in a bowl; coat with oil. Add mix; toss to evenly coat. Spread out on sheet pan. Bake until cooked through, 15–18 min.
Meanwhile, cut unpeeled potatoes into 2" pieces. Place in Multipurpose Steamer. Cover; microwave on high 8 min or until tender.
Add seasoning; mash potatoes, then stir in milk and butter. If needed, cover and microwave on high, 1 min or until warm.