Heat oil in a 4 to 5 quart heavy saucepan over moderately high heat until hot but not smoking, then saute onion, stirring, until golden, about 5 minutes. Add garlic, carrots, tomato, celery, cumin, and salt and saute, stirring, for 2 minutes. Add lentils, water, and broth and simmer, uncovered, stirring occasionally, until lentils are tender, about 20 minutes.
Stir in parsley and lemon juice; then season with salt and pepper.
Recipe courtesy Gourmet Magazine