Think of the pupusa as a more glorious quesadilla. The people of El Salvador flatten balls of corn dough (made of masa that's been treated with an alkaline solution) into flat filled cakes, each hiding a sliver of refried beans, pork, vegetables, and, more often than not, melted cheese, then heated until warm on the griddle. The end result's served piping hot with piquant curtido (pickled cabbage) and a thin red tomato-based salsa.
On a recent excursion to Balompie Café, the best pupusa I tried was a traditional version filled with cheese and loroco, a Central American flower bud that tasted a bit like bell peppers. If you love Latin flavors and have never laid eyes on the pupusa, it's a Salvadoran street food worth seeking out.