Meanwhile, scrub potatoes; place in single layer in 9-inch square microwavable dish. Cover with microwavable plastic wrap, folding back corner to vent steam. Microwave on High 5 to 6 minutes or until tender. Let stand 5 minutes. Cut potatoes in half; place on cookie sheet. Drizzle with butter. Sprinkle with 1/4 teaspoon salt and 1/4 teaspoon pepper. Top evenly with cheese. Broil 2 minutes or until cheese is melted. Sprinkle with onions.