Bring 1 cup water to a boil in a medium saucepan. Stir in long-grain rice. Cover,reduce heat, and simmer 20 minutes or until rice is tender and liquid is absorbed. Stir in plum tomato, chopped green chiles, black beans, corn, chopped green onions, and chopped fresh cilantro. Cook over medium heat, stirring constantly, until mixture is thoroughly heated.