Get the shrimp ready, defrost if frozen and pull their tails off.
Slice the starfruit horizontally.
In a small bowl, combine orange juice, rice vinegar, soy sauce, rice flour (or cornstarch) and powdered ginger. Stir well; there might be a few small chunks of flour left, but these will disappear when you combine with the rest of the ingredients.
Heat oil in a frying pan or wok, add garlic and stir-fry just until hot.
Add the shrimp and toss to coat with oil and vinegar; cook about 45 seconds to 1 minute, making sure to move the shrimp around the pan continuously.
6. Add sauce, then starfruit, and stir well. Cook for about 1 1/2 or 2 minutes, or until heated through. The sauce will thicken just a bit due to the flour or cornstarch; make sure it's thickened before you stop cooking.