Break eggs into a bowl and beat thoroughly. Add salt, sesame oil, oyster sauce, 2 tablespoons water and lightly beat until mixture is blended well. Set aside.
Heat wok or frying pan with 2 tablespoons cooking oil. Add egg mixture and use spatula to spread the eggs. Keep stirring until the eggs form curds. Gently break the curds into smaller pieces. As soon as the eggs are fully cooked, remove and set aside.
Add last tablespoon oil to wok/pan. Drop diced tomatoes and green onions into the pan and do a few quick stirs. Add sugar and last tablespoon of water to the tomato mixture. Cover and let it cook for about 45 seconds. Transfer the eggs into the tomato mixture, stir-fry for 30 seconds. Serve immediately. If desired, may be eaten with white rice.