Preheat the oven to 400 degrees F. Fold 4 sheets of parchment paper (16 1/2 by 24 1/2 inches) in half, and cut a half heart shape, away from the fold. Open the parchment paper to reveal a heart shape on a flat surface, and brush each with 1 tablespoon of olive oil. Season the salmon with salt and pepper. Place each salmon on half of the parchment sheet. Season the potatoes with salt and pepper. Place a layer of the potatoes on each salmon. Season the onions with salt and pepper. Secondly, place a layer of the onions over the potatoes. Season the tomatoes with salt and pepper. Thirdly, place a layer of the tomatoes over the potatoes. Next, place a layer of the preserved lemon over the tomatoes. Finally, lay the olives over the lemons. Sprinkle the top of each salmon with 1 tablespoon of the herbs. To close each bag, fold the second side of the paper over the salmon, fold the bottom edge over the top, and work your way edge over edge, folding and twisting, until the bag is sealed. Place each bag on a baking sheet and bake until the paper is puffed up and golden brown, for about 20 minutes. To serve, place a bag on each plate, slit the bag in an ?X?, and fold back the paper. Serve hot.