Stir together barbecued chicken, black beans, and 1/2 cup barbecue sauce in a medium bowl.
Place 1 tortilla in a lightly greased 10-inch springform pan, and spread with one-third chicken mixture. Sprinkle with one-third each of tomatoes, green onions, and cheese. Repeat layers twice. Top with remaining tortilla, and gently press. Cover pan with aluminum foil.
Bake at 400° for 15 to 20 minutes or until golden brown. Remove sides of pan, and cut into wedges. Serve with Avocado Mash and desired toppings. Garnish, if desired.