Combine first 4 ingredients in a 2-quart casserole. Cover with heavy-duty plastic wrap, and vent. Microwave at HIGH 4 minutes or until tender. Add sugar and next 6 ingredients (sugar through chiles), and stir well. Arrange chicken over the tomato mixture, and sprinkle with 1/4 teaspoon salt. Cover and microwave at HIGH 8 minutes. Rearrange chicken, spooning the tomato mixture over the chicken; cover and microwave at HIGH 8 minutes or until chicken is done. Remove chicken from dish; set aside, and keep warm.
Combine water and cornstarch, stirring until blended; add to tomato mixture. Microwave, uncovered, at HIGH 5 minutes, stirring after 2 1/2 minutes. Serve the chicken and tomato mixture over rice. Garnish with cilantro sprigs, if desired.