Step 1 Place the water and 1 teaspoon of salt in a 3-quart saucepan over high heat. When the water boils, turn the heat to low and slowly pour the rice into the water. Stir the rice in case any grains are sticking to the bottom, cover the pot and set a timer for 20 minutes. Check the rice after 5 minutes to make sure the heat is low and the water isn't boiling furiously.
Step 2 Cut the tomatoes lengthwise. Slice the core top off and discard. Put each half flat side down and cut each into about 4 strips lengthwise. Gently hold the strips together and cut in 1/4-inch pieces crosswise. Place the chopped tomatoes in a small bowl and sprinkle them lightly with salt. Sprinkle the tomatoes with vinegar and toss, either using your hands or a fork so the vinegar covers all the pieces. Set aside.
Step 3Slice off the root end of the onions and trim about 2 inches of the coarser green tops. Holding the green onions together, chop them crosswise into thin pieces, 1/8 th inch or less. Add them to the bowl with the tomatoes.
Step 4Remove the cilantro leaves from the stems; you need about 1 1/2 cups.
Step 5When the rice is done, taste a little. It should be tender, not firm. If it seems firm, cook it another 5 or 10 minutes and taste again for doneness. Stir in the tomatoes, onions, cilantro leaves and chiles. Taste and add salt and pepper if needed. Serve hot.