Seitan, tempeh, lentils, and beans w/ rice are the highest protein to calorie ratio foods I eat. Sprouted seed bread, most nuts/seeds, and most vegetables are pretty high in protein as well. I supplement with pea protein isolate to reach very high protein intake levels for bodybuilding purposes.
I think you probably know this, but whey is suitable for vegetarians (being a byproduct of curdling milk) - and whey-based protein supplements are often vegetarian. Vegan protein supplements are generally extracted from things like peas, beans or hemp.
I do know that, but thanks for clarifying. The word vegetarian in this case refers to being composed of only plant products. Maybe it can't be used that way.