I hate being vegetarian and eating meals without protein. I always wind up hungry soon after.
There are two appetizers--tofu salad and edamame--on their menu, either of which which would give your son his protein. I'm not sure if the tofu that they use in the salad is soft or firm, which could make a difference in whether it could hold up on the grill. If soft, it would probably turn out like scrambled eggs, which wouldn't be too bad. Or you could have them combine the edamame with the other vegetables on the grill.