Prepare the fillets: Check the red snapper for bones and remove any with a pair of tweezers or needle-nose pliers. Sprinkle with lemon juice and salt, and set aside.
Make the sauce: In a large, heavy skillet, heat 6 Tbs. of oil. Sauté the onions until soft, 6 to 7 min., over medium-high heat. Add the garlic and cook 1 min. Add the tomatoes and simmer 4 to 5 min. Then add the olives, capers, jalapeños, pickling juice, herbs, spices, chopped parsley, and fish stock or clam juice. Simmer uncovered for 7 to 8 min. Season with salt and pepper to taste, and set aside in a warm place.
Cook the fillets: In the same pan, heat 1/4 cup oil about 2 min., until it starts to shimmer. Sauté the snapper, skin side down, 2 min. and then turn over. Cover the fish with the tomato mixture. Bring to a simmer, cover tightly, remove from the heat, and let steam for about 3 min. With a slotted spoon, arrange the fillets on warm plates and spoon the sauce over them. Garnish with parsley.