1. Trim excess fat from meat. Place meat in a 4-quart Dutch oven; add any juices and spices from package. Add enough water to cover meat. Bring to boiling; reduce heat. Cover and simmer for 1-1/2 to 2 hours or until almost tender.
2. Meanwhile, trim tops of beets to 1/2 inch. Trim root ends. Add beets and potatoes to the corned beef mixture. Return to boiling; reduce heat. Cover. Simmer for 15 minutes or until potatoes and beets are tender.
3. Transfer meat to a cutting board. Thinly slice meat across the grain. Arrange meat and cabbage side-by-side on a large serving platter. Using a slotted spoon, remove potatoes and beets, and arrange next to the cabbage. For the dressing, in a small saucepan combine red onion, vinegar, olive oil or salad oil, spicy brown mustard, and honey; bring to boiling. Remove from heat. Drizzle over all. Serve with any remaining dressing. Makes 6 servings.