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.

77 Chinese & Vietnamese Cuisine also gets mentions from regulars, though without a specific address in the thread.

What this cluster of recommendations reflects is a real gap: the blocks immediately around the Ferry Building and Embarcadero Center run toward expense-account lunch options, and the affordable, counter-service Chinese-American spots are concentrated in Chinatown and the Tenderloin. Harborview Go fills a specific logistical need, but for the food the original poster described at the price point they probably had in mind, the walk to Stockton Street is the practical answer.