If you want to gain weight, try eating the various nut butters on buckwheat pancakes. For me, I ate "piles" of pumpkin seed butter. Pumpkin seed butter is also an anti-fungal. Ensure however that the p/s butter is not dry-roasted as that strips the anti-fungal power.
Also, use a lot of good oils. Try making the homemade mayonnaise and add it to various foods. I put it on salmon and greens. Yummy!!