This light omelet is cooked in a wok.
Heat a wok, without its stand, over high heat for 1 minute. Add 1/2 teaspoon oil, swirling to coat sides of wok. When hot, 1 minute, add tomatoes. Quickly stir until they soften, 1 to 2 minutes. Set aside tomatoes and juices. Rinse wok with hot water; dry.
In a medium bowl, whisk egg whites with 1 teaspoon salt until foamy, about 1 minute.
Return wok to high heat for 1 minute and add 2 tablespoons oil. When the oil is hot, about 1 minute, scoop up some of it using a large spoon; hold this oil over wok while you pour the whites into wok; immediately pour hot oil onto whites. Cook 1 1/2 minutes. Do not stir; egg whites will puff up. Add tomatoes with their juices in a circular pattern. Continue to cook until eggs are cooked through, 1 to 3 minutes. Sprinkle with remaining salt. Slide out of wok onto a serving plate, cut into wedges, and serve.