Combine first 6 ingredients.
Heat the oil in a Dutch oven over medium-high heat. Add onion and garlic; cook 15 minutes, stirring frequently. Add the cumin mixture, tomato, and juice. Reduce heat to medium, and cook 10 minutes, stirring occasionally.
Sprinkle chicken with 1/2 teaspoon salt. Add chicken and potatoes to pan; stir in chopped cilantro. Bring to a boil; cover, reduce heat, and simmer 50 minutes or until chicken is done. Serve mixture over rice, and garnish with cilantro sprigs.