In small bowl whisk together vinegar, mustard, oil, sugar, garlic and pepper. Set aside. Scrub potatoes. Halve potatoes or quarter any large potatoes. Cook, covered in boiling water, for 15 to 18 minutes or until just tender. Drain. Meanwhile, cook MORNINGSTAR FARMS VEGGIE ITALIAN STYLE SAUSAGE according to package directions. Cool slightly. Cut into bite-size pieces. In large bowl toss together warm potatoes, warm sausage pieces, arugula and onion. Drizzle with vinegar mixture. Toss just until coated. Serve immediately.