plain greek yogurtdiced avocado and pico de gallo for topping (optional)
Heat oil in a 10" non-stick skillet over medium heat. Add onion and sauteé for 1 minute. Add garlic and sauteé for an additional 30 seconds. Add beans, cumin and lime zest. Cook for an additional minute.
Remove pan from heat and mash beans with a potato ricer or masher. Stir in pico, goat cheese and cilantro.
Heat a 2nd non-stick pan (or clean original pan) over medium heat. Place a tortilla in the pan and spread half of the black bean mixture on the tortilla. Top with a second tortilla. Cook for 1 ½ to two minutes, until the tortilla is golden brown. Carefully flip and cook for an additional minute until both sides are golden brown.
Repeat the process with the remaining tortilla and black bean mixture. As the pan heats up you'll need less cooking time, so plan to flip the second quesadilla after about 1 minute.
Serve immediately with pico de gallo, greek yogurt and avocado (if desired)
The ideal way to reheat quesadillas is to put them back in a non-stick pan over medium-low heat for a few minutes so they crisp up again.