In large skillet over medium-high heat brown the ground beef, about 5-6 minutes. Drain fat. Add the onion and cook until they start to get tender. Stir in the steak sauce and beef stock, season with salt and pepper, bring up to a bubble and cook about 2 minutes.
Split open rolls, place one slice of cheese on one side and toast under broiler, keep your eye on them so they don't burn!
Place a scoopful of the meat on the bottom half of the bun, drizzle with additional steak sauce and place cheesy bun on top! Delish!