Bring a saucepan filled with water to a boil over high heat. Add the shrimp and cook for 3 to 5 minutes, until they are opaque and cooked through. Drain and place in a large ceramic bowl.

Place the noodles in a heatproof bowl and pour in boiling water to cover. Let stand for 10 minutes, until soft, then drain and rinse under cool running water. Add to the shrimp.

Cut the grapefruit into segments and add them and any juices to the bowl with the shrimp and noodles. Add the mint leaves.

To make the dressing, in a small bowl, whisk together all of the ingredients. Pour over the salad, toss gently to coat evenly, and serve at once.