Place oven rack in lower third of oven, and preheat broiler to high.
Combine first 8 ingredients in a medium saucepan, stirring with a whisk. Bring to a boil; reduce heat, and simmer 4 minutes. Stir in chicken; cook 1 minute or until heated. Remove from heat. Stir in tomato, sour cream, and avocado.
Stack tortillas; wrap stack in damp paper towels, and microwave at HIGH for 45 seconds. Spoon 1 cup chicken mixture into an 11 x 7-inch glass or ceramic baking dish. Spoon 1/3 cup chicken mixture in center of each tortilla; roll up. Arrange tortillas, seam sides down, in baking dish. Top with cheese. Broil 3 minutes or until cheese melts. Sprinkle with cilantro leaves.