Get the chicken ready: If you're not using chicken that's already cooked, cook your chicken breasts. You can boil them in water for about 15-20 minutes, or bake them in the oven at 375°F (190°C) for 20-25 minutes. The chicken is done when the inside temperature is 165°F (74°C). Let the chicken cool a little, then shred it with two forks or cut it into small pieces.

Chop the veggies: While the chicken is cooling, chop the celery and red onion into small pieces. Try to make the pieces the same size so they mix well in the salad.

Make the dressing: In a big bowl, mix the Greek yogurt, chopped dill, lemon juice, Dijon mustard, salt, and pepper. Stir it all together until it's smooth and creamy. Taste it and add more salt, pepper, or lemon juice if you want.

Mix it all together: Add the chicken, celery, and red onion to the bowl with the dressing. Gently mix everything together until the chicken and veggies are covered in the yogurt. Don't mix it too much, or the chicken salad might get mushy.

Chill it (you don't have to, but it's better): You can eat the chicken salad right away, but it tastes even better if you chill it in the fridge. Put plastic wrap over the bowl and chill it for at least 30 minutes, or even a few hours. This makes the flavors mix together better.