Preheat oven to 400 degrees.

In a skillet over medium high heat, add vegetable oil and onion. Saute for 1 minute and push to side. Add ground beef and cook for 7-8 minutes or until cooked though, breaking apart while cooking.

Add Worcestershire sauce, ketchup, brown sugar, salt, and pepper to skillet and mix well to combine with ground beef. Bring to a quick boil, then reduce heat and simmer, covered, for about 5 minutes; stirring occasionally. 

Using a large baking dish sprayed with nonstick spray, lay the bottom halves of the slider rolls across the bottom. Spread ground beef mixture over the top, then sprinkle cheddar cheese on top. Place the rolls tops on top of the cheese to close. Brush melted butter over the tops of the rolls, then sprinkle parmesan cheese over the top. 

Cover loosely with foil, then place into oven. Cook for 15 minutes, then remove foil carefully (steam will come out so be careful). Place back into oven for 5 more minutes.

Remove and allow 5 minutes to cool. Cut and serve immediately.