If you're really aiming to gain muscles fast and efficiently, it might also be a good idea to get a soy-based protein powder. Xtreme Antler This adds the extra proteins you need. It's important that the powder you're getting is of good quality with a high concentration of the essential amino acids.By following these guidelines you can easily gain muscles even if you want to keep a healthy vegetarian diet. Black beans are especially good for you as they are a complete protein. They have to soak overnight and it takes a few hours to cook them so i recommend that you do a large amount and put the leftover in the freezer. Having a black bean burrito is an excellent way to get your protein.