Preheat the oven to 400 degrees F. Combine the avocado's, lemon juice and garlic in a mixing bowl. Using a fork, mash the mixture until smooth but still chunky. Season the guacamole with salt and pepper. Spread 1/4 cup of the black bean puree on the bottom of one tortilla. Sprinkle 1/4 of the cheese over the black bean puree. Place a second tortilla on top of cheese. Repeat the process until all of the ingredients are used and you have four quesadilla's. Place the quesadella's on a parchment-lined baking sheet. Bake the quesadilla's for about 4 to 6 minutes or until the cheese has melted. Remove the pan from the oven and place on a cutting board. Slice each quesadilla into fourths. Garnish the quesadilla's with the guacamole, salsa and sour cream.