1In 10-inch skillet, heat 1 1/2 tablespoons of the oil and 1 tablespoon of the butter over medium heat until hot. Add onions and bell peppers. Cook about 10 minutes, stirring occasionally, until golden brown and tender. Remove skillet from heat and remove onion mixture from skillet; set aside.
2Toss beef with salt and pepper so seasonings are evenly distributed. To the same skillet, add remaining oil and butter and increase heat to medium-high. Add one-fourth of the beef and cook 1 to 2 minutes, turning once, until beef is browned. Remove beef from skillet, and repeat to cook remaining beef.
3Return beef to skillet with onions and bell peppers. Stir in Worcestershire sauce. Divide beef evenly among bottom halves of buns and spoon 3 tablespoons cheese dip onto each. Cover with top halves of buns. (If your cheese dip has been refrigerated, spoon it into a microwavable bowl and microwave 10 to 20 seconds on High or until warm).