Dice the chicken and place it in a medium bowl. Combine the cumin, salt and pepper in a small bowl; sprinkle over the chicken and toss to combine.
Heat a large, nonstick skillet to med-high heat. Add the chicken to the pan; sauté for 3 minutes. Add the onion, corn, and zucchini to pan; sauté for 2 minutes or until the chicken is done. Stir in the salsa and 2 tablespoons of the cilantro. Cook 2 minutes or until the liquid almost evaporates, stirring frequently.
TORTILLAS AND ASSEMBLY:
Working with 2 tortillas at a time, arrange them in a single layer on a baking sheet; lightly spray the tortillas with cooking spray. Broil for 2 to 3 minutes, or until very lightly browned.
Spoon about ¾ cup of the chicken mixture in the center of each tortilla; sprinkle each serving with ¼ cup of cheese. Broil an additional 2 minutes, or until cheese is melted. Repeat with the remaining tortillas and other ingredients.
Sprinkle each serving with a tablespoon of sour cream and a pinch of cilantro. Add a little chopped tomato too, if using. Serve immediately.