In medium saucepan, heat oil over medium heat; cook onion, leek, celery and garlic, thyme, salt and pepper, stirring until softened, about 4 minutes.
Add lentils, chicken broth and water; bring to boil. Reduce heat and simmer, adding more water if mixture dries out, until lentils are tender, about 25 to 30 minutes.
Stir in zucchini; cover and cook until zucchini is tender, about 5 minutes.
Meanwhile, brush salmon with oil; sprinkle with salt and pepper. Broil on foil-covered baking sheet, 3 inches (8 cm) from heat, until fish flakes easily when tested, about 6 minutes.
To serve, divide lentil mixture among 4 plates. Divide salmon and serve with lemon wedges.