To prepare salsa, combine first 7 ingredients. Cover and chill.
To prepare quesadillas, heat a large nonstick skillet over medium-high heat. Coat pan with cooking spray. Add 1/4 cup sliced onions to pan; sauté 3 minutes or until tender. Remove onions from pan; reduce heat to medium. Sprinkle 2 tablespoons cheese over each of 4 tortillas. Top each cheese-covered tortilla with one-fourth of onions, 1/2 cup turkey, 2 tablespoons cheese, and 1 tortilla.
Recoat pan with cooking spray. Add 1 quesadilla to pan; cook 2 minutes on each side or until lightly browned and cheese melts. Repeat with remaining quesadillas. Cut each quesadilla into 6 wedges. Serve with cranberry salsa and sour cream.