In a large skillet coated with cooking spray, saute the onion, celery and peppers in oil until crisp-tender. Add garlic; cook 1 minute longer. Stir in the chicken, soups, tomatoes and chili powder., Line the bottom of a 3-qt. baking dish with half of the tortilla strips; top with half of the chicken mixture and 1 cup cheese. Repeat layers. Bake, uncovered, at 350° for 30-35 minutes or until bubbly.