Preheat oven to 350 degrees F. Coat pork roast with the soup mix, place in a shallow pan and roast for 45 minutes, until meat thermometer inserted registers 155 degrees F. Remove roast from oven and let rest for 5 minutes. Scrape any pan drippings into a microwave-safe measuring cup; add water to measure 1/3 cup. Cover and microcook on HIGH for 20-30 seconds, until boiling. Place mushrooms in microwave-safe container, top with butter and cover with plastic wrap. Microcook on HIGH for 45-60 seconds until mushrooms are tender. Slice roast and place in rolls; spoon over mushrooms and some of the pan juices. Serve immediately.