Heat up one tablespoon of olive oil in a large pot over medium heat. Add the chopped onion, carrot, and celery to the pot sautéing until translucent, about 5-8 minutes.
Add the chopped tomatoes to the cooked vegetable mixture and cook for 3-4 minutes until the tomatoes soften slightly. Add the garlic and cook for 30 seconds until fragrant.
Add the rinsed lentils, bay leaf, and vegetable stock to the pot. Bring the soup to a boil. Then cover with a lid and reduce the heat to a simmer (low heat) for 20-25 minutes or until lentils are tender.
When the lentils are tender, add the oregano, cumin, and coriander along with some salt and pepper to taste. Let the soup cook on low, uncovered for about five minutes longer so the flavors can meld together.