I looked up most of the foods being mentioned here. I dont think Quinua, Black Beans, lentils, Etc... is what some one on a low-carb diet is looking for. While they are good sources of protein, the fact is they are way to Carb-negative. For example 1 cup of Quinua will yield 118g carbs and 15g protein. Usually HPLC diets want to get 30-50 of calories from protein.
However Edamame that was mentioned above seems to be a really good source of protein yielding 16g protein and only 15 carbs per cup. That is very impressive for a vegetable. Now I just hope they taste good