In a large sauté pan, heat oil over low heat, add garlic and cook and stir until golden, about 3-5 minutes. Raise heat to medium, add vegetables and cook and stir until nearly tender (time will depend on type of veggies used). Add black beans, corn and hot sauce and cook and stir about 4-5 minutes more.
Set vegetables aside in a bowl and clean the skillet. Heat to medium-high, and when hot place a tortilla in it. You do not need oil. Sprinkle about ¼ cup of the grated cheese or cheese substitute evenly on tortilla. Add some of the filling, some of the diced white onion and optional cilantro, another thin layer of cheese and finally another tortilla.
Cook until bottom tortilla is slightly browned and bottom layer of cheese starts to melt. Flip over and brown other side. The layers of cheese should act like glue to hold the quesadilla together.
Remove from pan and let cool a few minutes on a flat surface or cutting board. Cut in quarters or in small wedges and serve with optional toppings/dips.