In a small bowl, combine the sour cream, cilantro and lime juice; set aside. Heat barbecued beef according to package directions. Spread four tortillas with refried beans; top each with 1/2 cup beef and 1/4 cup cheese. Top with remaining tortillas.
In a large skillet coated with nonstick cooking spray, heat quesadillas over medium heat for 1-2 minutes on each side or until lightly browned. Cut each into four wedges. Serve with shredded lettuce, sour cream sauce and tomatoes if desired.