Cover potatoes with water in 4-quart saucepot; bring to a boil over high heat. Reduce heat to low and simmer 14 minutes or until potatoes are tender; drain and cool slightly.
Combine Hellmann's® or Best Foods® Real Mayonnaise with mustard in large bowl. Add potatoes and onions and toss gently. Season to taste, if desired, with salt and ground black pepper. Serve chilled or at room temperature. Just before serving, sprinkle with bacon if desired.