Heat grill to high. Clean and lightly oil hot grates. Season steaks with salt and pepper and cook 3 to 4 minutes per side for medium-rare. Transfer steaks to a plate, tent with foil, and let rest.
Meanwhile, place a double layer of foil or a grill topper on grill. Top with tomatoes and scallions; drizzle with oil. Grill until tender and lightly charred, 6 to 8 minutes. Transfer vegetables to a bowl, toss with vinegar, and season with salt and pepper. Top steaks with vegetables.