1. Preheat the oven to 425º F.
2. Bring 4 cups of water plus 1 teaspoon salt to boil. Stir in lentils, reduce heat and simmer uncovered for 20 to 25 minutes, until lentils are tender, stirring occasionally. Drain lentils and set aside.
3. While the lentils cook, section the grapefruit. Using a sharp knife, remove the top and bottom peel, including all of the white pith, to expose the flesh. Cutting down the sides from top to bottom, remove the peel completely, so all that remains is the fruit. Carefully cut along the side membrane to remove each individual section of grapefruit. Reserve the remaining membranes and flesh for the vinaigrette.
4. To make the vinaigrette, squeeze the remaining grapefruit membrane and flesh over a strainer to remove the excess juice. Add two tablespoons grapefruit juice to a bowl with white wine vinegar, olive oil, Dijon mustard and whisk to combine. Season to taste with salt and pepper.
5. Combine warm lentils, baby arugula and chopped Italian parsley in a large bowl. Dress with vinaigrette and season with salt and pepper.
6. Line a baking sheet with foil and season salmon portions with salt and pepper. Wrap each skinless salmon filet with one piece of prosciutto, tucking the ends underneath the salmon portion. Drizzle each piece lightly with olive oil and roast in the center of the oven 6 to 8 minutes, until prosciutto crisps and salmon is flaky yet still moist.
7. Serve salmon portions with lentil salad and grapefruit sections. Enjoy!