Heat the oil in a large pot over high heat. Add the onions, jalapeŇos, and mangoes and sautČ for 30 seconds. Stir in the green onions, 1/2 cup of the water, the lime and lemon juices, vinegar, sugar, salt, and pepper. Bring to a boil, lower the heat, and simmer for 5 minutes.
Meanwhile, combine the cornstarch with the remaining 2 teaspoons water. Stir the cornstarch mixture into the pot, bring to a boil, and cook for 1 to 2 minutes. Remove from the heat. Serve immediately or store, refrigerated, in an airtight container for up to 24 hours. Reheat in a saucepan over low heat.
Yield: 2 cups