Preheat oven to 425°.
Combine 1/4 teaspoon salt, chili powder, and cumin in a small bowl. Place tortilla strips on a cookie sheet coated with cooking spray; sprinkle with half the cumin mixture. Bake at 425° for 15 minutes or until tortillas are crisp and lightly browned; cool on a wire rack.
Combine remaining cumin mixture and chicken in a zip-top plastic bag; shake to coat. Heat a large nonstick skillet coated with cooking spray over medium-high heat. Add chicken; cook 3 minutes on each side. Add julienne-cut green and red bell pepper and sliced onion; cook 4 minutes or until vegetables are tender, stirring frequently.
To make dressing, combine lime juice, olive oil, and 1/4 teaspoon salt in a large bowl; stir with a whisk. Combine lime-juice mixture and lettuce; toss well. Divide lettuce evenly among 4 plates; top each with chicken mixture, tomatoes, and baked tortilla strips.