1. For olive relish, stir together olives, 1/2 cup celery, 1 tablespoon juice, the onion, 1-1/2 teaspoons thyme, and 1 teaspoon oil in a bowl; salt and pepper to taste.
2. Bring 6 cups water to boil with lentils in a large saucepan and simmer until lentils are tender, about 20 minutes. Drain well and transfer to a bowl. Stir in remaining 1/4 cup celery, 2-1/2 tablespoons juice, 1-1/2 teaspoons thyme, the parsley, goat cheese, and 2 tablespoons olive oil; salt and pepper to taste. Keep warm, covered.
3. Rinse chicken and pat dry; season with salt and pepper. Heat remaining 1 teaspoon oil in a large nonstick skillet over moderately high heat until hot but not smoking. Add chicken and cook, turning once, until golden brown and cooked through, about 17 minutes. Transfer chicken to a cutting board and let stand 5 minutes. Cut chicken crosswise into 1/4-inch-thick slices and serve over lentils. Top with olive relish. Makes 6 servings.