Chopped Cajun Ahi Tuna Salad

Name: Chopped Cajun Ahi Tuna Salad
Ingredients: 8 ounces fresh or frozen ahi tuna steaks, thawed; 1 tablespoon salt-free Cajun seasoning, such as Frontier® brand; Nonstick cooking spray; ¼ cup light ranch salad dressing, such as Hidden Valley® brand; 3 cups bite-size pieces romaine lettuce; ¼ cup quartered cherry tomatoes; ¼ cup chopped celery; ¼ cup chopped green sweet pepper; ¼ cup sliced green onions