For the chargrilled pepper and mushrooms, toss the pepper and mushrooms together in a bowl with the olive oil, then season with salt and freshly ground black pepper. Heat a griddle pan until smoking, add the pepper and mushrooms and fry for 3-4 minutes, or until tender and charred on all sides. Set aside.
For the refried beans, place all of the beans ingredients into a mini food processor and blend to a smooth paste.
For the quesadilla, place one tortilla in a heated frying pan, spread over half of the refried beans and scatter over half of the chargrilled pepper and mushrooms. Place another tortilla on top and spread over the remaining refried beans, followed by the rest of the pepper and mushrooms. Finish with the third flour tortilla on top, press down and cover with a lid. Cook over a medium heat for five minutes, or until the bottom tortilla is golden-brown.
To serve, slide the quesadilla onto a serving plate and slice into wedges. Serve.