In a small bowl, add the lime juice, soy sauce, coriander, and cayenne pepper, then whisk to combine. Pour over the shrimp and toss to coat. Set aside and start making the coconut rice while the shrimp marinates. Peel and chop the mango into small chunks while the rice is cooking, set aside until ready to serve. Cook the shrimp when the coconut rice is almost finished cooking, during the last 5 minutes.