Step 4. Mix in the vegetable broth and reduce the heat to a gentle simmer. Simmer, partially covered, for about 15 minutes, or until the lentils are al dente.
Step 5. Stir in the diced tomatoes and cook until warmed through. Optional:Transfer about one-half of the soup to a large blender and blend until smooth. Add the puréed soup back to the saucepan.