Saute onions until translucent, about 5 minutes. Add a pinch of salt or two. Then add corn from the frozen bag and use about double for the amount of onion you use. Cook for 5 minutes. Add the same volume of chopped spinach plus. When its cooked add some crumbled feta. The more Feta you add, the more salty and flavorful it will get.
Put some on a flour tortilla which is on a
Comal or pan to cook the quesadilla. Add Mexican cheeses and fold over. Wait a couple of minutes and flip. Serve by itself or with chopped cilantro and your favorite salsa.