Welcome to HCM,
If you want to gain weight, your diet should be balanced. It should contain all (Proteins
, Carbohydrates, Fats, Minerals & Vitamins
) in sufficient quantity. The diet of vegetarians is generally not balanced particularly in respect to proteins. For proteins we require amino acids, but essential amino acids can not be synthesized by our body. Thus your diet should contain all essential amino acids. Pulses are good source of proteins, but all essential amino acids are neither present in pulses nor in cereals. We can get all essential amino acids if our meal contains both(Cereals & Pulses). Our every meal usually contains cereals, but lacks in pulses. Thus add pulses to your every meal in sufficient quantity. Being male, it will be better for you to try for a masculine body rather than fat. So you should regularly workout for sufficient time.
Wish you good health,