I'm not vegan but I have been vegetarian for a long while. The main thing that makes being vegetarian/vegan so hard with this fetish is that most of that food just doesn't have that many calories so you have to find little work arounds and just eat in as large of quantities as you can stomach. I would suggest trying to find a good protein powder/mass gainer (I don't know any vegan brands off the top of my head) and make a bunch of weight gain shakes with that and peanut butter (I've found I prefer soy milk for shakes if I do a milk alternative but really any of them should work). Then for meals just try to find things that are heavy in carbs and try to eat as much as you can. For a nice simple meal one of my favorites is refried beans on rice with cornbread.
3 months