Heat oil a medium sized pan over medium heat.
Add onions and a pinch of salt and saute until softened and slightly caramelized about 5 minutes.
Add in zucchini and corn and another pinch of salt and pepper.
Saute another 6-8 minutes until softened but still slightly firm then stir in the black beans and set aside.
While the vegetables are cooking, make the avocado dipping sauce by combining the avocado, pinch of salt, pepper and lime juice in a food processor.
Process until very smooth and set aside in a small bowl.
Heat a large nonstick skillet on medium heat.
Add a tortilla to the pan and allow to warm 30 seconds.
Sprinkle on some of the cheese and a few spoonfuls of the vegetable mixture.
Top with another soft tortilla and press the quesadilla down with a spatula.
Using the spatula to help guide you, turn over the quesadilla carefully to warm on the opposite side (as you would a grilled cheese sandwich).
Repeat until desired amount of quesadillas are made.
Slice the quesadilla in half (or quarters) and serve with dipping sauce and extra lime if desired.