Place the lemongrass, all but 2 tablespoons of the cilantro, 1/2 cup of the mint, 1/2 cup of the oil, garlic, jalapenos, paprika, and salt in a food processor or blender and process until smooth. Add the remaining 1/2 cup of oil and vinegar and process until smooth. Place the fish fillets in a large baking dish, cover with the mojo and turn to coat. Marinate fish for up to 1 hour.
Place 4 (16-inch) long pieces of parchment paper on your work surface with the short half facing you. Crease each down the middle. Place a fillet in the center of the bottom half of the rectangle and pour about 1/4 cup of the mojo over each fillet and sprinkle with the remaining 2 tablespoons of cilantro. Fold the top half of over the fillet so that the top and bottom edges meet. Tightly crimp and fold the edges of the parchment working from 1 end around to the other to seal the package. Place the packets on a baking sheet and bake for 9 to 10 minutes for 3/4-inch thick fillets or up to 12 minutes for 1-inch thick fillets.
Place the fish packets on a large serving dish and open the packets tableside. Serve with juices from the packet and sprinkled with the chopped cilantro and mint leaves.