Preheat oven to 350 degrees F. In a very hot skillet sear beef in 1 teaspoon of oil, about 30 seconds per side, or until just browned. Season with salt and black pepper. Stuff meat into open bread loaf. Top with cheese and bake until bread is slightly crispy and cheese is melted. Meanwhile, heat remaining oil in the same skillet and saute onions until tender. When sandwich is ready, top sandwich with onions. Serve with potato chips.