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 an even layer in the prepared baking dish.
Place the shredded chicken in a bowl and add 1/2 cup of the BBQ sauce. Toss until the chicken is evenly coated.
Spread the barbecue chicken evenly over the bottom buns. Spoon the remaining BBQ sauce over the chicken.
Sprinkle the mozzarella, smoked Gouda, sliced red onion, and 1 tablespoon of chopped cilantro evenly over the chicken. Finish with freshly ground black pepper to taste.
Place the top halves of the buns over the filling.
Cover the baking dish with foil and bake the BBQ Chicken Sliders for 15 minutes.
Meanwhile, melt the butter and stir in the remaining tablespoon of chopped cilantro.
Remove the foil and brush the cilantro butter over the tops of the buns.
Return the sliders to the oven uncovered and bake for about 10 minutes, or until the tops are golden and the cheese is thoroughly melted.
Let the baked chicken sliders rest for a few minutes, then separate and serve warm.