Cook the Pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente.
Drain and rinse under cool water to stop cooking. Shake off excess water well.
Season the Chicken: If using precooked chicken, toss it with 1 teaspoon Cajun seasoning and a drizzle of olive oil. If cooking from raw, season chicken breasts with 1 tablespoon Cajun seasoning, sear in a skillet with a little oil, and cook through.
Let rest, then dice or shred.
Make the Dressing: In a large bowl, whisk together ranch, Greek yogurt or mayo, lemon juice, garlic, and 1 tablespoon Cajun seasoning. Taste and adjust salt, pepper, and heat (cayenne or hot sauce) as you like.
Add the Veggies: Stir in bell pepper, red onion, celery, corn, and tomatoes. Fold in the herbs.
Combine: Add the cooled pasta and chicken to the bowl.
Toss gently until everything is evenly coated. If using cheese, fold it in now.
Adjust and Rest: Taste and add more Cajun seasoning, lemon, or salt as needed. Let the salad rest for 10–15 minutes so the flavors mingle.
If chilling, cover and refrigerate for at least 30 minutes.
Serve: Garnish with extra herbs or a pinch of Cajun seasoning. Serve cool or at room temperature.