Prep the chicken: If using rotisserie, remove skin and bones, then shred or chop into bite-sized pieces. Aim for small, even pieces for the best texture.
Make the avocado base: In a large bowl, add the avocado flesh.
Mash with a fork until mostly smooth, leaving a few small chunks for texture.
Add flavor: Stir in lime juice, olive oil, garlic, cumin, salt, and pepper. Taste and adjust the seasoning now so the whole salad is balanced.
Fold in the mix-ins: Add chicken, red onion, cucumber, celery, tomatoes, and herbs. Gently fold until everything is coated but not mashed.
Finish and serve: Taste again and add more lime, salt, pepper, or red pepper flakes if you like heat.
Serve right away on toast, in lettuce cups, or with crackers.