Heat a large skillet or frying pan on medium-high heat with canola oil and add in sliced onions. Cook for 10-15 minutes stirring occasionally.
Add sherry or red wine vinegar once the onions start to darken and move them to one side of the pan.
In the same pan, add the full amount of Hillshire Farm Ultra Thinly Sliced Roast Beef on the other side of the caramelized onions and cook for 2-3 minutes until the beef is hot to the touch. Next, cover the beef with Swiss cheese and continue to cook in the pan until the cheese just starts to melt.
Split the French rolls and toast in the pan with the onions and roast beef.
Place the warm roasted beef and melted cheese inside the toasted French roll and generously top it with the onions.
Quickly deglaze the pan with beef stock and pour into a small bowl for dipping.