Heat oil in a medium saucepan over medium-high heat. Add leek, carrot, and garlic; sauté 2 minutes. Stir in lentils, water, and broth; bring to a boil. Cover, reduce heat, and simmer 25 minutes or until lentils are tender and liquid is nearly absorbed. Remove from heat. Add celery, parsley, vinegar, 1/2 teaspoon salt, and 1/4 teaspoon pepper to lentil mixture, stirring to combine.
Sprinkle trout with remaining 1/4 teaspoon salt and 1/4 teaspoon pepper. Place fish on a baking sheet coated with cooking spray; broil 5 minutes or until fish flakes easily when tested with a fork. Break fish into chunks; add to lentil mixture, tossing gently to combine.