I haven't made this, Andrea, but I watched Michael Chiarello make it the other day...
He stuffed the onions inside the shoulder--in the cavity left by boning, and it looked like he served it sliced. I'm sure if you shredded it the onion stuffing would mix in nicely, or if you haven't included the onions yet, they would make a nice garnish afterwards.
The FoodTV recipes are always so tersely written. I wish they'd give a bit more detail--maybe they want you to tune in and/or buy the books to see how you're supposed to serve things