So cooking mostly from scratch, I simplify on beans for time with 4 small kids.
I fried the platanos in mantequlla (butter) with garlic and salt them while cooking.
I put the beans and the cheese in the pupusa and attempt to keep them for oozing out.
I made a large mess and they turned out very gordo (fat) instead of thin like they Honduras make them. They were ok, no one starved.
It definitely helped have the fresh tomatoes, onion and cilantro on top.
The platanos were good, they would have been excellent with chocolate drizzled on top (assuming I did not cook with the garlic)