Being vegetarian is not problem to increase weight.list of food items wont help u to gain weight. U need proper planned diet and exercise regime to gain muscle mass as u need to gain muscle not fat. What is your height and weight

Avoid junk foods,add extra calories to your diet,have 4 to 5 meals rather than large 3...add protein rich foods and healthy fats to diet for e.g..egg white...add fibre rich foods like green leafy veggies,carrots,Apple, etc. Add green tea to your diet .you have to eat more foods high in amino acids,calcium, zinc, iron, copper and magnesium...do regular exercise without failure......consult dietitian for further details