Begin by shredding the rotisserie chicken into a mixing bowl. Fold in the chopped celery, radishes, red onion, and fresh dill. Add the mayonnaise and dill mustard, then season with salt and pepper to taste. Mix thoroughly until all ingredients are well combined.

Next, preheat your oven to 375°F (190°C).

Roll out the thawed puff pastry sheets on a lightly floured surface, aiming for an even thickness. Use a cookie cutter or a wine glass to cut the pastry into circles, making them larger than the desired slider size.

With a beaten egg in hand, gently brush the tops of each pastry circle. Bake in the preheated oven for 15-20 minutes or until they are puffed up and beautifully golden.

Once the puff pastry rounds have cooled slightly, carefully slice the tops off the baked pastries. Spoon a generous amount of the creamy chicken salad into the bottom halves, then add a few arugula leaves or sprouts for a fresh crunch.

To secure your sliders, you can spear them with toothpicks. If desired, garnish with small olives.