1. Cut the snapper fillets into pieces about 1 inch long and 1/2 inch wide.
2. Do not use pieces any larger than that, as they will not be properly cooked by the citrus juices.
3. In a large glass bowl, marinate the fish in the lime and lemon juices.
4. Cover and let sit for one hour.
5. Chop the chiles, removing any seeds, and soak the chiles in a bowl of cold water.
6. Julienne the red onion and soak in another bowl of cold water.
7. Add the chiles and onion to the fish, mix well and refrigerate for an hour before serving.