To prepare curry, heat oil in a large nonstick skillet over medium-high heat. Add onion and 1/2 teaspoon salt. Cook 2 minutes or until onion is tender, stirring occasionally. Stir in tamarind; cook 2 minutes, stirring to break up tamarind. Add ginger and next 5 ingredients (through cinnamon); cook 2 minutes, stirring frequently. Add remaining 1/2 teaspoon salt, potato, water, milk, and tempeh; bring to a boil. Cover, reduce heat, and simmer 15 minutes or until potatoes are tender. Uncover; stir in juice and soy sauce. Simmer 3 minutes or until slightly thickened. Discard cinnamon stick.
To prepare rice, cook rice according to package instructions, omitting salt and fat. Stir in cilantro and 1/4 teaspoon salt. Serve with curry.