Place chicken between 2 sheets plastic wrap and gently pound to even thickness. Sprinkle both sides with taco seasoning. In large frypan, place 1 tablespoon butter over medium heat. Add chicken and cook about 3 minutes per side; set aside to cool. In small bowl, mix together mayonnaise, sour cream, cilantro, red pepper flakes and the reserved 1-1/2 teaspoons taco seasoning. On sheet of wax paper, mix together Parmesan cheese and cornmeal. Place bread on wax paper; spread tops lightly with l/2 mayonnaise mixture and sprinkle evenly with Parmesan mixture. Turn bread and spread other side with remaining mayonnaise mixture. Place 1 chicken breast half on each of 4 slices. Top with jalapeno jack cheese, onion, tomato sprinkled with salt and avocado sprinkled with lemon pepper. Place bread slice on top with coated side up. In frypan, place half of remaining butter; add sandwiches to frypan and grill until light brown. Add remaining butter, turn sandwiches and grill other side. Cut sandwiches in half; fasten with wooden picks. Arrange on serving platter lined with lettuce leaves and small bowl of Mango Salsa in center. Garnish with tomato wedges and cilantro sprigs.
Mango Salsa: In medium bowl, mix together 2 peeled and cubed mangos; 1/4 julienned red bell pepper; 3 green onions, chopped; 1/2 jalapeno pepper, seeded and chopped; 4 teaspoons lemon juice; and 2 tablespoons chopped cilantro. Cover and chill.