Preheat oven to 400 degrees F. Coat both sides of tortillas with nonstick cooking spray. Place on baking sheets. Bake for 7 to 9 minutes or until lightly browned. Transfer to wire racks to cool. Tortillas will crisp up as they cool.

Meanwhile, in a large skillet combine broth, chili powder, cumin, and oregano. Bring to boiling. Add chicken; return to boiling. Reduce heat and simmer, covered, for 8 to 10 minutes or until chicken is no longer pink (170 degrees F). Remove from heat. Let chicken cool in the liquid about 15 minutes or until cool enough to handle. When cool enough to handle, transfer chicken to a cutting board and shred the chicken into large pieces using two forks. Return shredded chicken to the cooking liquid.

In a medium bowl combine beans, corn, tomato, onion, snipped cilantro, lime juice, and pepper.

Place tortillas on serving plates. Top with lettuce and bean mixture. Using a slotted spoon, spoon chicken atop bean mixture. If desired, garnish with cilantro and serve with sour cream and lime wedges. Makes 6 tostadas.