To prepare the steak: Remove the steak from the refrigerator. Pat dry with a paper towel and season each side with 1 teaspoon kosher salt. Let sit at room temperature for 30 minutes. Pat the steak dry again with a paper towel and sprinkle lightly on both sides with kosher salt.
To sear the steak: Preheat a 12-inch heavy-bottomed cast-iron skillet over high heat for 3 minutes. Add the rice oil, swirl the pan to distribute evenly, and then let heat for about 1 minute, until the oil begins to smoke. Place the beef in the pan and press down gently with a spatula for 1 minute. Cook for 4 to 6 minutes, depending on the thickness. Flip the steak and cook for 4 to 6 minutes longer for medium-rare (127°F on an instant-read thermometer). Transfer the steak to a cutting board and season with salt and pepper if desired. Let rest for at least 5 minutes while you cook the spigarello.
To cook the spigarello: Pour off the steak oil from the pan, give the pan a wipe, then reduce the heat to medium and add 3 tablespoons olive oil. Let the oil heat for 1 minute. Add the spigarello and 1 teaspoon salt and cook, stirring occasionally, for 2 minutes. Add the garlic and cook for 1 minute longer. Move the spigarello to one side of the pan and slide that side of the pan off the heat. Add the remaining 1 tablespoon olive oil and the cherry tomatoes to the other side of the pan still over the heat and cook, shaking the pan slightly to turn them, for about 2 minutes, until the skins pop and the tomatoes are warm.
To serve: Cut the steak against the grain into 4 uniform pieces. Divide the spigarello and tomatoes evenly among individual serving plates and top with the steak. Pour any remaining steak juices over each serving, then sprinkle with the sel gris and serve.