Cook the brown rice in water on the stovetop according to package directions. It typically takes 45 minutes, so start the rice first, then prepare the rest of the meal.
Make sure your Dutch oven supports the weight of your bamboo steamer. Fill the Dutch oven ⅔-¾ of the way full with water. Bring it to a boil over medium heat.
Prepare your banana leaves by rinsing well and patting dry. Cut the leaves into 12-14" lengths. Trim the tough end off of each leaf, but save the ends.
To make a cod packet, take two banana leaves and place one perpendicularly over the other (i.e., make a cross shape). Place 3 citrus slices in the middle of the packet. Lay one fish fillet on top. Sprinkle with 1 teaspoon of lime juice, ½ tablespoon of fresh basil, and salt and pepper to taste. Repeat with the remaining packets.
To wrap your packets, you will need to make four folds. Wrap the right edge of the leaf over the seasoned fish. Now wrap the left edge of the leaf over the fish, so it is snug in the packet. Fold the bottom edge of the packet under, and tie closed with a reserved tough leaf end (or you can use kitchen twine). Finally, fold the top edge of the packet under, and secure by tying closed with a tough leaf end. Place the packet in your bamboo steamer, and wrap the remaining fish packets. (Watch the recipe video, it will be helpful!)
After all of your packets are wrapped, tied, and placed in the steamer, put the cover on the steamer. Carefully place the steamer on top of your Dutch oven that contains the boiling water. Steam the packets over medium heat for 15-20 minutes, until the fish flakes easily with a fork. The exact steaming time will depend on the thickness of the fish pieces that you start with.
While the packets are steaming, make the watermelon cucumber salads. Stir the watermelon cubes, cucumber chunks, lime juice, lime zest, and mint together. Let it macerate while the meal finishes cooking.
To serve, divide the cooked rice between three plates. Carefully open the cod packets and place the fish on the rice. (The banana leaves are for flavor only, they do not get eaten!) Serve the cucumber watermelon salad on the side. Add a squeeze of juice to your cooked cod from the lime wedges, if desired. Enjoy!