Hello,
Welcome to icliniq.com.
I understand your concern.
Please mention your height, age, and weight. Make sure you are completely healthy and not suffering from any disease. Get a complete body checkup, including a complete hemogram which may rule out many conditions that might be interfering with your tendency to gain weight. Moreover, if genetically you are lean, nothing much can be done about it. However, it would be best if you took a balanced nutritious, healthy diet high in proteins. Here is an example of a diet rich in protein. You may modify the same as per your taste. You can have four boiled, scrambled, or omelet eggs for breakfast. The white part of the egg mainly contains albumin, a protein. Drink a glass of milk (at least one liter of full cream milk split at your convenience) with two to three scoops of protein powder. A bowl of chicken soup can be taken at midday. For lunch, a big bowl of black gram, green gram, or any other pulses. Also, you can have cottage cheese, fresh paneer, soybean, fish, chicken, or mutton with 3 to 4 chapattis (this may increase as per your appetite) made out of multi-grain flour, a bowl of curd, and a glass of buttermilk. In the evening, have a glass of juice with a few snacks (made out of besan/gram flour which is protein-rich). Before dinner, take a bowl of soup (chicken, mutton, or vegetable).
For dinner, you can eat vegetables (choose from the list mentioned above) with two to three chapattis and a bowl of curd. You may try different vegetables with high protein recipes like soybeans, pulses, and beans. Drink soya milk which will give you added proteins. Fish has high omega-3 fatty acids. Please do not overconsume the proteins, as they have to break down for digestion, and appropriate levels of uric acid must be maintained in the body. Water left over from making paneer can be used to make many different things, including adding it to food. Various recipes made out of hung curd are protein-rich.