If using raw chicken, grill or cook it in a skillet until fully cooked, then shred it into pieces.

In a large mixing bowl, combine the diced celery, red bell pepper, green onions, and cherry tomatoes.

In a separate bowl, whisk together the mayonnaise, lemon juice, Dijon mustard, salt, and black pepper until smooth.

Add the shredded chicken to the bowl with the vegetables, then pour the dressing over the top. Mix well to combine.

Garnish with chopped parsley if desired, and serve chilled or at room temperature.