In a 5- to 6-qt. Dutch oven heat 2 tsp. of the oil over medium. Add chicken; cook and stir until no longer pink. Remove from pan. Cover and chill until needed.
In Dutch oven heat remaining 2 tsp. oil over medium-high. Add corn and stir fry vegetables; cook and stir 3 minutes. Stir in the next five ingredients (through salt). Bring to boiling; reduce heat. Simmer, covered, 30 minutes or until tortillas break down and broth is slightly thick. Stir in chicken. Simmer, uncovered, 5 minutes more.
Sprinkle servings with cheese and green onions. If desired, top with yogurt and jalapeño pepper and serve with lime wedges.