Brush both sides of bread with 1 tbsp oil. Whisk remaining oil with vinegar in a large bowl. Add tomatoes, olives, onion and salt. Season with pepper. Let stand 20 min.
Oil grill, then toast bread, with lid open, until grill marks form, 2 min per side. Transfer to a cutting board and cut into bite-sized cubes. Stir bread along with basil into tomato mixture. Serve with Grilled t-bone with lemony maître d’ butter.