In a large skillet over medium heat, add olive oil. Sauté the diced onion and bell pepper until they soften, about 3 to 4 minutes.
Add the minced garlic and sauté for another 30 seconds until fragrant.
Stir in the black beans, corn, cumin, chili powder, salt, and pepper. Cook for an additional 3 to 4 minutes, until everything is heated through.
Remove the skillet from heat. If desired, stir in vegan cheese until melted slightly.
In the same skillet (or a clean one), place a tortilla and spoon a portion of the black bean mixture onto one half of the tortilla. Fold the tortilla in half.
Cook on medium heat for about 2 to 3 minutes until the bottom is golden and crispy. Carefully flip and repeat on the other side for an additional 2 to 3 minutes.
Remove from heat and repeat the process with the remaining tortillas and filling.
Cut the quesadillas into wedges and serve warm, garnished with fresh cilantro and alongside salsa if desired.