To prepare vinaigrette, combine first 3 ingredients; stir with a whisk. Set aside.
To prepare the quesadillas, drain beans through a sieve over a bowl, reserving 1 tablespoon bean liquid; discard remaining liquid. Combine 1/2 cup beans and 1 tablespoon reserved bean liquid in a small bowl; mash with a fork. Reserve remaining beans. Spread bean mixture evenly over 4 tortillas. Sprinkle each with 1/4 cup cheese and about 1 tablespoon jalapeño; top with remaining tortillas.
Heat a large nonstick skillet coated with cooking spray over medium heat. Cook quesadillas for 4 minutes on each side or until golden brown. Remove the quesadillas from the pan, and cut each into 4 wedges. Combine vinaigrette with lettuce, and toss well. Arrange 1 1/2 cups lettuce mixture on each of 4 plates. For each serving, spoon 3 tablespoons reserved beans over lettuce mixture, and place 1/2 cup tomato over the beans. Top each serving with 1/4 cup salsa, 2 tablespoons chopped onion, and 1 tablespoon sour cream. Serve each with 4 quesadilla wedges.