Form the beef into eight 3-inch patties.
Heat the oil in a large skillet over medium-high heat. Season the patties with ½ teaspoon salt and ¼ teaspoon pepper and cook until an instant-read thermometer inserted in the center of each patty registers 130ºF, 2 to 3 minutes per side for medium-rare.
Form sandwiches with the rolls, ranch dressing, lettuce, tomato, and burgers. Serve with the cut-up vegetables.