Preheat the oven to 350°F (175°C).
In a mixing bowl, combine the shredded chicken and barbecue sauce until evenly coated; set aside.
Stir together the melted butter and garlic salt in a small bowl; set aside.
Using a sharp knife, slice the Hawaiian rolls in half horizontally and arrange the bottom halves in a baking dish in a single layer.
Spread the BBQ chicken mixture evenly over the bottom halves of the rolls.
Arrange the thinly sliced red onion over the chicken, then place the sliced cheddar cheese evenly on top.
Cover with the top halves of the rolls, then use a pastry brush or spoon to brush the melted garlic butter over the tops, allowing some to run between the rolls.
Bake for 20–30 minutes, or until the cheese is melted and the tops are lightly golden.
Remove from the oven, garnish with chopped cilantro if desired, then cut between the sliders and serve warm.
