Preheat your oven to 375°F (175°C).
Brown the ground beef in a skillet over medium heat, breaking apart into crumbles, until fully-cooked. Drain excess fat, if needed.
Return the cooked beef crumbles to the skillet and stir in 15 ounces of Manwich (or equivalent of homemade sloppy Joe sauce) until fully combined. Remove from heat.
On a foil-rimmed sheet pan, cut the slider buns in half, horizontally, keeping the bottom buns attached and the top buns attached (if possible).
Layer each bun evenly with the meat sauce. Spread the cheese across the meat evenly.
Place the other half of the buns on top, creating sandwich sliders.
In a bowl, whisk together melted butter, garlic powder, onion powder, salt, pepper, and parsley.
Using a basting brush or spoon, spread the butter & herb mixture generously over the tops of the dinner rolls or buns.
Optionally, sprinkle French onions over the sliders for added texture and flavor.
Cover the baking dish with aluminum foil and bake in the preheated oven for about 10-12 minutes, or until the sliders are heated through and the cheese is melted.
Remove from the oven and let them rest for a few minutes before serving. You may need to gently run a knife through the sandwiches - at the natural divisions of the rolls - to ensure the sliders will pull apart easily.