Heat the olive oil in a large pan over medium heat.
Add the chopped onion, garlic, carrot, and celery. Sauté for about 5 minutes until the vegetables soften.
Add the chopped mushrooms and sauté for another 5 minutes until they release their moisture and start to brown.
Stir in the canned lentils, crushed tomatoes, dried oregano, dried basil, dried thyme, salt, and pepper.
Simmer the sauce for about 15-20 minutes, stirring occasionally, until it thickens. Adjust the seasoning to taste.