In a large bowl, combine the cooked chicken, halved red grapes, diced red onion, and diced celery.

In a small bowl, whisk together the mayonnaise, lemon juice, salt, garlic powder, onion powder, and black pepper. Taste and adjust seasoning with additional salt and pepper if needed, starting with small amounts.

Pour the dressing over the chicken mixture and stir until everything is evenly coated.

Serve immediately, or store in an airtight container in the refrigerator for 3 to 5 days. Discard any leftovers that have been left out at room temperature for more than 2 hours.