Combine chicken, 2 tablespoons cilantro, and pepper in a small bowl; stir well.
Combine tomato sauce and water; pour into a plate. Set aside.
Microwave 2 tortillas, uncovered, at HIGH 10 seconds; dip each tortilla in sauce mixture. Spoon 1/4 cup chicken mixture down center of each tortilla; top each with 2 tablespoons black beans and 1 tablespoon cheese. Roll up tortillas, and place seam sides down in an 8-inch square baking dish coated with cooking spray. Repeat procedure with remaining 2 tortillas, sauce mixture, chicken mixture, black beans, and cheese.
Pour any remaining tomato sauce mixture over enchiladas; top with remaining black beans and remaining cheese. Bake, uncovered, at 375° for 20 minutes or just until bubbly. Sprinkle with remaining 1 tablespoon cilantro. Serve with sour cream.