Heat a large skillet over medium heat and add the garlic and green onion and cook for about 30 second, stirring often.
Add the beans, water, salt and spinach and cook until the water is absorbed, about a minute or two.
Take the mixture out of the skillet, transfer to a bowl and mash with a fork.
Add the miso and stir until the miso is incorporated into the mixture.
Add salt and pepper to taste.
Once the Bean Mixture is ready, assemble the quesadillas.
Spread a generous amount of the mixture on a tortilla, cover it with another tortilla and heat the quesadilla in a dry skillet on both sides, until they are slightly browned.