Place 2 1/2 cups water, lentils, and bay leaf in a medium pot over medium-high heat. Bring to a light boil, lower the heat to a simmer, and allow the lentils to cook through, about 30 minutes, adding more boiling water if necessary. You should see just a few bubbles coming to the top to ensure they don’t go mushy. Refrain from adding salt until they’re finished, or they’ll remain crunchy. When four or five lentils are cooked through (no crunch but still intact), drain of any remaining liquid and discard the bay leaf.
When 10 minutes are left on the lentils, drizzle the olive oil into a large frying pan over medium heat. When the oil is hot but not smoking, add the onion, capers, olives, and preserved lemons. Stirring often, cook until the onion is just beginning to caramelize.
Add the garlic and red pepper flakes, and continue to sauté for 2 more minutes.
Stir in tomatoes, gin, vermouth, and lemon juice. Lower the heat and simmer for 4 minutes.
Add the cooked lentils, taste, and add salt and black pepper, if necessary. Remove from the heat and stir in the parsley.
As the vegetables and lentils cook, fry your fish. Drizzle the vegetable oil into a medium frying pan over medium heat. Pat dry the fish fillets, using a paper towel, and season generously on both sides with salt and black pepper. Place the salmon, skin side down, in the hot pan. Cook for 4 to 5 minutes, until the skin is crispy, then turn and cook for a further 3 to 4 minutes. Remove from the heat and let rest for 3 minutes before serving on the lentils. Garnish with fresh lemon wedges.