do you like the taste of peanut butter?
because fat from nuts is a very healthy source of fat for the body, naturally low in carbs if you want to stay lean, and high in protein.
or if you just want to gain weight for the sake of gaining weight, eat a ton of fruit; very high in carbs, and carbs that is not used by the body is converted to fat and stored away.
i'm trying to gain 20-30 lbs, i buy a box of kirkland soy milk from costco, and blend it with 2tbsp of peanut butter, i don't really measure it, i just get a huge scoop of what looks like 2, possibly 3 (maybe even 4?) spoons of pb. blend it. drink it. lift some weights. etc. oh then i also drink muscle milk after lifting. does it help? i don't know, i barely started lifting a week ago, but the pb+soy i've been doing awhile just to replace solid foods at nights, or breakfast if i have no time to sit and eat (because i woke up late or fell asleep in the shower.)