1) Heat the oil in a nonstick frying pan over a high heat. Saute the onion slices until wilted and just starting to take on some colour, stirring all the while, about 7 minutes. Sprinkle the onions with salt while cooking.
2) Slice the silverside beef into very thin slices; partially freezing the meat enables you to slice it very thinly.
3) Remove the onions from the pan. Salt and pepper the steak slices and then saute them in the same frying pan in batches until cooked through, about 45 seconds per side. Repeat the process for the remaining steak slices, replenishing the oil as needed.
4) Meanwhile, melt the cheese cubes in a microwave-safe bowl on low power for a couple of minutes or until completely melted.
5) Cut each roll down the middle lengthwise. Fill each roll with a good helping of steak slices and top with the melted cheese and sauteed onions.