Cook the chicken breast using a poaching or grilling method until the internal temperature reaches 74°C (165°F).

Remove chicken from heat and allow it to cool completely at room temperature or chilled.

Dice the cooled chicken into 1cm cubes.

In a large mixing bowl, whisk together the Greek yogurt, Dijon mustard, lemon juice, salt, and black pepper until smooth.

Add the diced chicken, celery, and red onion to the bowl.

Fold the ingredients together with a spatula until the chicken is thoroughly and evenly coated.

Incorporate the fresh dill and adjust seasoning if necessary.

Transfer to airtight containers and refrigerate for a minimum of 30 minutes before consumption.