Heat olive oil in a large skillet or Dutch oven over medium heat. Add chopped onion and sauté for 5-7 minutes until softened and translucent.

Add minced garlic and cook for another minute until fragrant.

Stir in ketchup, apple cider vinegar, brown sugar, Worcestershire sauce, smoked paprika, chili powder, garlic powder, onion powder, Dijon mustard, salt, and black pepper. Bring the sauce to a gentle simmer.

Add the chicken breasts/thighs to the simmering sauce. Ensure the chicken is mostly submerged. If the sauce is too thick, add a splash of chicken broth.

Reduce heat to low, cover, and let simmer for 20-25 minutes, or until the chicken is cooked through and easily shreddable with a fork.

Remove chicken from the skillet and place on a cutting board. Using two forks, shred the chicken into bite-sized pieces.

Return the shredded chicken to the skillet with the BBQ sauce. Stir to coat completely. Let it simmer uncovered for an additional 5-10 minutes, allowing the sauce to thicken slightly and the flavors to meld. Taste and adjust seasoning if needed.

In a large mixing bowl, combine the shredded cabbage and grated carrot.

In a separate small bowl, whisk together mayonnaise, apple cider vinegar, granulated sugar, Dijon mustard, celery seed (if using), salt, and black pepper until smooth.

Pour the dressing over the cabbage and carrot mixture. Toss well to ensure all vegetables are evenly coated.

Cover the bowl and refrigerate for at least 15-20 minutes to allow the flavors to meld and the coleslaw to chill.

Preheat a skillet or griddle over medium heat. Lightly brush the cut sides of the hamburger buns with melted butter.

Place the buns cut-side down on the hot skillet/griddle and toast for 1-2 minutes until golden brown and slightly crispy.

To assemble, place a generous scoop of BBQ pulled chicken onto the bottom half of each toasted bun.

Top the pulled chicken with a spoonful of creamy coleslaw. Add dill pickle slices if desired.

Place the top half of the bun on top and serve immediately.