Step 1

Heat a 10-inch skillet over medium-low heat.

Step 2

Stir in the oil and onions, season with salt and pepper and cook until slightly brown, turning occasionally about 15 to 17 minutes.

Step 3

Slice the bread open, place 3 oz of cooked roast beef on each piece and top with 1/4 of the caramelized onions.

Step 4

Top with cheese and place in the broiler for 1 to 2 minutes to melt the cheese, careful not to burn it.