Make the filling:

1. Heat oil in a large skillet over medium-high heat until the hot oil sizzles, about 1 minute. Add onion and garlic and sauté until fragrant, about 1 minute.
2. Add bell pepper and jalapeño and sauté until tender, about 2-3 minutes.
3. Add black beans and season with cumin, paprika, salt, and pepper. Mix well and cook until beans are heated through, about 2-3 minutes.
4. Stir in cilantro and remove the skillet from the heat. Transfer the black bean veggie filling to a bowl and set aside.

Assemble the quesadillas:

1. Heat a clean skillet over medium-low heat for 1 minute and brush with a little bit of oil.
2. Place one tortilla in the pan. On one half of the tortilla, sprinkle 1/4 cup cheddar cheese, top with 3 tablespoons of the black bean filling, and top with another 1/4 cup cheddar cheese.
3. Fold the empty half of the tortilla over to create a half moon. Cook until the tortilla is crispy and the cheese melts, about 2 minutes per side.
4. Repeat with remaining tortillas.
5. Transfer the quesadillas onto a plate and slice into 3 triangles. Serve with sour cream, guacamole, and/or salsa if desired.