Cook the lentils: In a large saucepan, combine the lentils, pork butt, onion, carrot, and bouquet garni and cover with water by 2 inches. Bring to a boil, reduce the heat and simmer, covered, until tender, 20 to 30 minutes. Reserve 3/4 cup of the cooking liquid, drain the lentils, discard the vegetables and pork, and set the lentils aside.

Cook the vegetables: Heat the olive oil in a large skillet over medium heat. Add the carrot and turnips, season with salt and cook, stirring occasionally, until just tender, about 5 minutes. Transfer to a small bowl and return the skillet to medium heat. Melt the butter, add the bacon, and cook until almost crisp. Transfer to paper towels with a slotted spoon and set aside. Pour off all but 2 tablespoons of the fat. Add the shallot and garlic to the pan and cook for 1 minute without browning. Add the reserved lentils, sauteed vegetables, bacon, and reserved lentil broth; simmer until the broth has been completely absorbed by the lentils, 3 to 5 minutes. Season with salt and pepper and keep warm.

Cook the salmon: Position an oven rack about 6 inches from the broiler and a second rack in the center of the oven. Heat the broiler on high. Line a rimmed baking sheet with foil and brush the foil lightly with some of the melted butter. Lay the salmon fillets, skin side down, on the foil; brush the tops and sides generously with the remaining butter and season with salt and pepper. Broil the salmon on the upper rack until the top is nicely browned, about 8 minutes. It should feel fairly firm when pressed with a fingertip and be slightly translucent in the middle if flaked. It will continue to cook a bit on its own once out of the oven, but if it's still a little rare, turn off the broiler, immediately turn the oven on to 400 degrees F, move the baking sheet to the center rack, and shut the oven door. Bake the salmon until just done, 1 to 2 minutes. Mound the lentils and vegetables on warm dinner plates and set a fillet on top. Garnish with the parsley and serve at once.