Combine chicken, barbecue sauce and chiles in a large, nonstick saucepan; bring to boil.
Reduce heat and simmer, covered, until chicken is tender and cooked through, about 25 minutes Remove from heat and let cool.
Meanwhile, combine tomatoes. onion, chopped cilantro, garlic, vinegar, oil, and salt in medium bowl until blended. Set aside.
Preheat oven to 425 degrees. Spray a large, nonstick baking sheet with nonstick spray.
Place tortillas on baking sheet. Spread each with the beans, then top with then top with the chicken mixture, scallions, and cheese. Bake until the cheese is melted and bubbly, about 15 minutes Top each tostado with the tomato mixture, sour cream and additional cilantro, if desired.