Rub the swordfish with the remaining grapeseed oil and season with salt and pepper, to taste. Grill the swordfish until grill marks appear on both sides, about 3-4 minutes per side. Once the tomatoes have cooled slightly, drizzle with extra-virgin olive oil, to taste.
Cut the swordfish into slider-sized portions (you may want to cut parallel to the work surface as well to make them thinner). Place in the buns, topped with some pickled onions and the charred cherry tomatoes.