Preheat the oven to 375˚F (190˚C). Grease 2 baking sheets with nonstick spray and line with parchment paper.
Make the cornbread: In a medium bowl whisk the buttermilk, eggs, and melted butter until smooth.
In a large bowl, combine the flour, cornmeal, salt, sugar, baking powder, and baking soda, and whisk to combine.
Add the wet ingredients to the dry ingredients and mix until fully incorporated.
Divide the batter between the prepared baking sheets, and use a spatula to smooth the top.
Bake for 15 minutes, until golden brown.
Meanwhile, make the barbecue sauce: Add the ketchup, Worcestershire, apple cider vinegar, Dijon mustard, paprika, brown sugar, and black pepper to a medium saucepan over medium heat and whisk to combine. Bring the sauce to a boil, then reduce the heat to low and simmer for 10 minutes.
Make the coleslaw: In a large bowl, add the mayonnaise, Dijon mustard, pepper, apple cider vinegar, paprika, and salt, and whisk to combine.
Add the green cabbage, red cabbage, and shredded carrots, and stir until fully coated.
Add the shredded chicken to a large bowl, and pour the barbecue sauce over the chicken, stirring until fully coated.
Invert one of the cornbread sheets onto a large cutting board and peel off the parchment paper. Spread the chicken over the cornbread in an even layer. Top with the slaw. Invert the other cornbread sheet on top of the slaw and peel off the parchment paper.
Slice into 12 equal pieces. Top each piece with 2 pickle slices and secure with toothpicks.