why would you gain weight--unless you are dangerously thin. if it s about appearance, it s stupid to do something like that for vanity. why risk clogging your arteries and hurting your health just cause you are sick of being thin. let your body maintain it s natural weight--it s what s best for your own body.
eat eat eat, thats all we can say. I wouldn t load yourself with alot of fried foods, because that s just unhealthy....but eat alot of carbs and protein. If you can get in about 1/2 to 1 gram (protein and carbs) per pound of body weight you want to be then that should help. Also the times you eat. Eat late at night and as soon as you wake up to stop your fasting cycle...hence break-FAST. Good luck!
Start workout, and take supplements.