(If you have cooked chicken on hand, skip this step.) Lightly sprinkle chicken breasts with Cajun seasoning. Bake for 20 minutes at 350 degrees F (I do this in my toaster oven) or cook on both sides in a hot skillet until cooked through. Allow to cool slightly.
Shred or dice cooked chicken into small bite-sized pieces.
In a medium bowl, stir together mayonnaise, Ranch dressing, and sriracha. Stir in chicken and green onions. Squeeze quartered tomatoes to leave most of the seeds and juice behind, and stir tomatoes into salad.
Serve over salad greens, on buns, or wrapped in tortillas.