Beans + rice caontains all the amino acids, I'm told. As a matter of fact, any legume plus any grain is supposed to be good. The vegetarian world lives on it, primarily. Oh, learn Indian cooking! Fabulously scrumptious, and vegetarian! I recommend any cookbook by Madhur Jaffrey. It might be a little bit of a challenge to stay at 20g, but remember most Americans heat hundreds of grams a day, if not thousands, not mere tens. Declare yourself on OWL, and I bet you can find ways to eat extremely healthily and get sufficient protein, at a reasonable number of grams per day.
"Time and trouble will tame an advanced young woman, but an advanced old woman is uncontrollable by any earthly force." --Dorothy L. Sayers