Preheat the oven to 350°F (175°C). Line a 9x13-inch baking dish with parchment paper and lightly coat it with nonstick cooking spray.
Arrange the bottom halves of the slider buns in the prepared baking dish.
In a bowl, combine the shredded chicken with ½ cup of the BBQ sauce until evenly coated.
Spread the chicken mixture over the buns. Drizzle the remaining BBQ sauce evenly across the chicken.
Sprinkle mozzarella, smoked Gouda, sliced red onion, and half of the chopped cilantro over the chicken. Season with black pepper.
Place the top halves of the buns over the filling.
Cover the dish with foil and bake for 15 minutes.
Meanwhile, melt the butter and stir in the remaining cilantro.
Remove the foil, brush the tops of the buns with the cilantro butter, and continue baking uncovered for 10 minutes, or until the tops are golden brown.
Serve the BBQ Chicken Sliders warm while the cheese is perfectly melted.