In a large pot over high heat, bring the water to a boil. Add the lentils, turn the heat to medium-low, partially cover, and cook for 15 minutes. Drain and place the lentils in a large mixing bowl. Toss with ¼ teaspoon of salt and let cool completely.
In a medium-sized saucepan over medium heat, toast the walnuts, moving them around the pan every now and again for 4 minutes. Place on a cutting board, letting them cool slightly, and roughly chop. Set aside.
Mix the French Dressing into the lentils, stirring well to combine. Add the dill, goat cheese, lemon zest and juice. At this point your salad can be refrigerated for up to 3 days. When ready to serve, add the walnuts and arugula. Taste and adjust seasoning, then serve with the extra crumbled goat cheese sprinkled on top in your favorite bowl or platter.