Combine first 4 ingredients in a small bowl and stir until blended.
Heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Place 1/4 of the chopped chicken over half of 1 tortilla. Sprinkle with 1/4 of the cheese, 1/4 cup of black beans and 2 tablespoons of green onion mixture; fold in half and cook 2 minutes on each side or until lightly browned. Place quesadilla on baking sheet and put in oven to keep warm. Repeat procedure with remaining quesadillas. Cut each quesadilla in quarters. Serve with salsa, avocado slices, any remaining onion mixture and sour cream.