Cook the pasta: Bring a large pot of salted water to a boil. Cook pasta until just al dente.
Drain and rinse briefly under cool water to stop cooking. Shake off excess water well.
Prep the chicken: If using rotisserie or leftover chicken, chop or shred into bite-size pieces. If cooking fresh, season lightly with salt and pepper and grill or pan-sear until cooked through, then let it rest before chopping.
Make the avocado dressing: In a food processor or bowl, combine avocados, Greek yogurt, olive oil, lemon juice, garlic, and a pinch of salt and pepper.
Blend or mash until smooth and creamy. Taste and adjust with more lemon or salt as needed.
Add herbs and heat: Stir in chopped herbs and red pepper flakes (if using). The herbs should look speckled throughout the sauce.
Combine the salad: In a large bowl, add the cooled pasta, chicken, tomatoes, cucumber, and red onion.
Spoon the avocado dressing on top and toss gently until everything is well coated.
Finish and season: Sprinkle in Parmesan if using. Taste and adjust with more salt, pepper, or lemon juice. The flavors should be bright and balanced.
Serve or chill: Serve immediately for the creamiest texture, or chill for 30–60 minutes to let flavors meld.
Give it a quick toss before serving.