Set oven to 250° F.
If adding veggies, place sliced mushrooms, minced onions, and minced red peppers into a medium-hot skillet. Cook until they start to soften, stirring occasionally.
Add the chopped spinach and the black beans. Turn the heat down to low and cover the skillet. Cook until the spinach is wilted.
Drain liquid and set aside.
Heat a large skillet on medium-high. Add butter, ½ tablespoon at a time.
Place a flour tortilla in the skillet. Add a ½ cup cheese and 1-2 tablespoons veggie mixture. Fold the tortilla over. Grill until golden brown (watch carefully).
Flip the tortilla over and grill the other side until golden.
Remove the quesadilla from the skillet and place on a baking sheet. Keep warm in the oven until all of the quesadillas are finished.
Repeat until all tortillas are filled and grilled.
Serve with optional toppings.
Makes 6 quesadillas
If desired, try our cashew-tofu sour cream recipe and our guacamole.