Juliehafrancis, my suggestion is go to a supermarket or healthfood store and buy a ready made nut roast that can be shoved in the oven. Rose Elliot has some great recipes for celebration roasts but do you want the hassle? Don't make your life more stressful.
I am a veggie as are dh, dd & ds and we are going out to my Mums for Christmas lunch but I am making our own celebration nut roast and we will have what everyone else has. This simplifies everything. I won't cook meat so I figure I can make her life easier this way. Mum won't be cooking the roast potatoes or gravy in animal fat.