Finely dice the celery stalks into 1/4-inch pieces and dice the red onion into similar-sized pieces. Halve the red grapes lengthwise so they're easier to eat throughout the salad. Strip the fresh dill leaves from the stems and roughly chop them. Set all prepped ingredients aside in separate piles. I like to prep the vegetables first because getting them uniform in size ensures even texture throughout the salad.

In a large mixing bowl, whisk together the mayonnaise, Dijon mustard, celery seeds, smoked paprika, and lemon juice until smooth and well combined. The lemon juice helps brighten the mayo-based dressing and adds acidity to balance the richness. Taste the dressing at this stage and adjust the mustard or lemon juice if needed—you want a well-seasoned base before adding the other ingredients.

Add the diced cooked chicken to the dressing base and fold gently to coat evenly. Then add the prepped celery, red onion, halved grapes, and chopped fresh dill. Fold everything together carefully using a rubber spatula, being gentle with the chicken so it stays in nice chunks rather than breaking apart. I prefer folding over stirring because it keeps the salad texture intact and prevents the chicken from getting shredded.

Season the entire salad with salt and black pepper to taste, starting with a light hand and adding more gradually as you mix. Taste after each addition and adjust as needed. Chill the salad for at least 30 minutes before serving to let the flavors meld together and the salad to develop more cohesive taste.