Evenly slice the attached rolls in half horizontally. Place the bottom half into the baking pan or on the baking sheet.
Spread an even layer of the burger sauce on top, about 3-4 tablespoons. Evenly layer (4) slices of colby jack cheese over the rolls. Spoon over the ground beef filling and top with the caramelized onions. Sprinkle remaining cheddar cheese and mozzarella (optional) over the onions. Evenly layer the remaining (4) colby jack cheese slices on top.
Spread a layer of burger sauce over the top half of the rolls, about 3-4 tablespoons. Carefully, place on top of the colby jack cheese slices.
In a small bowl, mix together the butter, parsley and salt to taste. Generously brush the top of the rolls with about half of the butter mixture.
Bake for 12-15 minutes (if using a baking sheet) or 15-20 minutes (if using a baking pan). If the cheese is not fully melted, add the sliders back into the oven for an additional 5-10 or until the cheese is melted to desired consistency.
Mix in minced garlic (optional) into remaining butter mixture and brush over hot slider buns. Serve immediately while still hot. Enjoy!