Place ham bone in a 4-qt. slow cooker. Add peas, celery, carrot and onion. Combine water, beer and mustard; pour over vegetables. Cook, covered, on high 5-6 hours or until peas are tender., Remove ham bone from soup. Cool slightly, trim away fat and remove meat from bone; discard fat and bone. Cut meat into bite-size pieces; return to slow cooker. Stir in remaining ingredients. If desired, top with minced parsley.