I made this tonight for dinner and fell in love. Please used the stewed tomatoes! Lately I have been using shallots in the place of onions because I have a ton of them. Sorry for the weird amount on the butter beans; I use about 3/4 of a 15 oz can. If you want it a little more like a marinara try adding some tomato paste. Celery would also be good in the sauce. I like to serve this in bowls with about 1/2 pasta 1/2 sauce in them, so you may need to adjust pasta and mushrooms for what you like. Be careful as to how much cheese you use too! Hope you enjoy as much as I did!