you may gain weigh, by eat more frequent, more carbs, more protein, and increase fat quality,
for your information, fat help you to "resist" your nutrition absorption. because all the bad fat ( saturated, trans).

And if you wanna gain more muscle, you may add 2-3 days gym routine which concentrate on muscle gaining program,

protein powder not really necessary needed, it's "supplement food"
not food substitution,
naturally you can get enough protein amoun (2gram/kg body weight)
by consuming fish, chicken, meet, and sprout.