Heat oil in a large saucepan over medium heat. Add onion, carrots and celery. Cook, stirring occasionally, 10 min., or until onion starts to brown. Add garlic and cook 1 min., until golden.
Pour vegetable broth, diced tomatoes and 2 cups (500 mL) water into saucepan. Stir in red lentils. Bring to a boil over high heat then reduce to a simmer; cover and cook 30 to 40 min., or until lentils and vegetables are tender.
Stir in parsley. Divide soup into bowls. Garnish with additional parsley to serve.