1. Lay a tortilla on your work surface. Scatter half the cheese, then half the beans over one side. Fold the tortilla in half over the filling. Repeat with the second tortilla.
2. Warm a wide, heavy pan over medium heat. Pour in 1/2 teaspoon oil and tilt the pan to spread the oil around.
3. Put a quesadilla in the pan and cook until browned underneath, about 1 1/2 minutes. Flip it, then cook it until it's browned on the other side and the cheese is melted, about 1 1/2 minutes longer. Transfer it to a plate and repeat with the second quesadilla.
4. Cut each quesadilla into wedges and serve immediately with salsa, sour cream, and guacamole.