Coat food rack with cooking spray; place on grill over medium-high heat (350 to 400).
Place chicken on rack, and grill 10 minutes on each side or until done.
Shred chicken, and place in a large bowl. Stir in 1 can tomatoes with green chiles, half of black beans, and 1 cup of cheese.
Spoon chicken mixture evenly down center of each tortilla; roll up tortillas, and place, seam sides down, in a 13- x 9-inch baking dish. Top with enchilada sauce and remaining tomatoes with green chiles, black beans, and cheese.
Bake at 350 for 30 minutes.
Remove from oven, and let stand 10 minutes. Top each serving with avocado slices and sour cream.