Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced onion and sauté for about 3-4 minutes until translucent.
Add the minced garlic, bell pepper, and zucchini to the skillet. Sauté for another 5 minutes until the vegetables are tender.
Stir in the corn and black beans. Season the mixture with cumin, chili powder, salt, and pepper. Cook for an additional 2-3 minutes until everything is heated through. Remove from heat.
On half of each tortilla, sprinkle a layer of shredded cheese, then spoon a generous amount of the veggie mixture over the cheese. Top with an additional sprinkle of cheese and fold the tortilla in half.
In another skillet, heat the remaining tablespoon of olive oil over medium heat. Carefully place the folded quesadilla in the skillet, cooking for about 3-4 minutes on each side, or until golden brown and crispy. Repeat with remaining tortillas.
Once cooked, remove the quesadillas from the skillet and let them cool for a minute before cutting them into wedges.
Garnish with chopped cilantro and serve with salsa and sour cream on the side.