Heat the oven to 375°F. Brown beef, onion and pepper in a skillet for 7 to 8 minutes until the meat reaches 160°F, breaking it into fine crumbles; drain excess fat.
Stir in ketchup, tomato paste, Worcestershire, mustard, brown sugar, water, salt and pepper. Simmer for 8 to 10 minutes until thick enough to mound.
Slice the connected rolls horizontally as one slab. Place the bottom half in a snug baking dish and distribute the hot filling evenly across it; replace the top slab.
Mix melted butter and garlic powder and brush over the rolls. Cover loosely with foil and bake for 10 minutes.
Uncover and bake for 4 to 5 minutes until the tops are golden. Rest for 5 minutes, then cut between rolls; each slider counts as one serving.