Combine the first seven ingredients in a bowl. Spread one side of two of the tortillas with the refried beans. Sprinkle and spread the bean-topped tortillas with the cheese/vegetable mixture; top with the remaining two tortillas. Heat the oil in a large skillet set over medium heat. Cook one of the stuffed tortillas 2-3 minutes per side, or until golden brown and cheese is melted. Keep warm in a low oven until the other is cooked. Cut the quesadillas into wedges and serve with salsa and, if desired, sour cream.