In a large pot, heat the olive oil over medium heat. Add the onion and garlic and cook until softened, about 5 minutes.
Add the carrots, zucchinis, and bell peppers to the pot. Cook for another 5 minutes, until the vegetables start to soften.
Stir in the diced tomatoes, lentils, vegetable broth, and dried herbs. Season with salt and pepper to taste. Bring to a boil, then reduce heat and simmer for 1 hour, or until the lentils are tender.