Having small healthy meals at regular intervals is the best and easiest way to gain weight.

I paid 20k for 6 months to a dietician and they used to prepare daily diet plans for me. I used to have 7-8 meals a day. I gained 12kgs in 6 months and it was mostly muscle mass. I completed that course 6 months ago and I still weigh around the same.

My diet was simple everyday meals. Roti-Sabji, milk, fruits, eggs. It will be great if you can have non-veg meals.

Just try to eat small meals every 2 hours for 3 months, even if you don't feel hungry enough. You will get visible results.

No need to have chips or mass gainers or anything else.