Heat oven to 375°F. Spray 13x9-inch (3-quart) glass baking dish with nonstick cooking spray. In medium bowl, combine tomatoes, zucchini, onions and beans; mix well. Reserve 1/3 cup enchilada sauce; set aside. In another medium bowl, combine remaining enchilada sauce and sour cream dip; blend well.
Spoon 2 tablespoons enchilada sauce mixture in bottom of sprayed baking dish. Arrange 8 tortilla pieces over sauce, overlapping as necessary. Spoon half of vegetable-bean mixture over tortillas; sprinkle with 2/3 cup of the cheese. Spoon half of remaining sauce mixture over cheese. Repeat layers, reserving 2/3 cup cheese for top. Top with reserved 1/3 cup enchilada sauce. Cover with foil.
Bake at 375°F. for 30 to 35 minutes or until thoroughly heated. Uncover; sprinkle with reserved 2/3 cup cheese. Bake, uncovered, an additional 5 minutes or until cheese is melted. Let stand 10 minutes before serving. Sprinkle with cilantro.