I assume since you're a 140 pounds and in school that you don't have a lot of $ to work with. Cheap Asian dishes will make you gain weight for real cheap. Chicken, rice, pork (especially fatty cuts), broth, cabbage, onions, and whatever else you want for seasoning and sauces will get you looking like a big boy pretty quick.
You can also go the neckbeard WH40k diet of meatbread and cup noodles. Gotta watch your salt intake doebeit; too much with too little water will make you feel like shit. Don't get used to food with high caloric counts either or you'll become meximutt IRL.