The stronger answer, according to regulars on r/AskSF, is to walk ten to fifteen minutes into Chinatown. Stockton Street between Broadway and Pacific has several steam-table and plate-lunch operations — Wing Sing Dim Sum is the most cited — where a single-entree or three-item box runs cheaper and the volume is higher. The California Cable Car or the 1-California bus covers the distance if you don't want to walk.

For something farther afield but well-regarded, Emperor's Kitchen at Larkin and Turk comes up repeatedly: cheap, big portions, the Chinese-American format the original post was describing. That puts it in the Tenderloin, a different errand than a lunch break from the Embarcadero.