In a saucepan; combine lentils, carrots, garlic, bay leaf and thyme. Add enough water to cover by at least 1 inch (2.5 cm). Bring to boil; reduce heat and simmer, uncovered, for 15 to 20 minutes or until lentils are tender.
Drain, discarding bay leaf.
Transfer lentil mixture to bowl. Add onion, celery, parsley, oil, lemon juice, salt and pepper. Toss to mix. Let cool to room temperature.