How to gain weight on a vegan diet?

Not for me- no no, I am trying to lose weight. My husband, however, is trying to gain, and he just keeps losing. Anyone have any tips on how to properly gain on a vegan diet (also gluten-free)?

Nuts?  nut butters, add pulverized nuts to recipes will enhance flavor and add fat calories.  cashews are good (I buy them raw and they are like pure cream)

Yeah, I am going to start adding oils and nuts to his food for extra calories. I hope it helps!