I would skip the mash potatoes.
YUM! I used homemade seitan for this recipe and it was delicious. My husband, who is a meat eater, LOVED this. I used yellow onion instead of shallots and no black olives or parsley (didn't have either on hand) and it was still yummy. We had the green beans on the side, but loved the sauce so much we wished there was enough for the beans! Definitely make extra sauce- you'll want it!