In a medium saucepan, combine the uncooked lentils with 2 1/2 cups of water. Bring to a boil, then reduce heat to simmer; cover and cook for 15 minutes. Turn off heat and allow the lentils to steam for another 5 minutes; drain and let cool.

In a medium bowl combine the lentils, shallot, grapes, dill, walnuts, lemon juice, lemon zest, vinegar, 1 tablespoon olive oil, arugula, 1/4 teaspoon salt and pepper to taste; set aside.

Heat oven to broil and move rack to the highest position. Sprinkle trout fillets with lemon zest, remaining salt, and 1/4 teaspoon pepper; brush with olive oil. Broil the trout for 4-5 minutes. Serve with lentil salad.