Soak lentils in hot water for at least 15 minutes while preparing and chopping the veggies.
Place the lentils in a strainer and rinse with cold water; set aside.
In a deep pan or heavy-bottomed pot, sauté the onion, carrot, celery, mushrooms, and a pinch of salt over medium-low heat. Sauté for about 5-7 min, stirring from time to time to prevent burning. When the onion is translucent and lightly brown, add a few spoons of water to deglaze the pan. Then add the garlic, Italian seasoning, salt, pepper, and sauté for 30 sec to 1 min, stirring frequently.
Pour the drained lentils, tomato paste, crushed tomatoes, vegetable broth or water, and bay leaves. Stir to combine.
Bring the sauce to a simmer, cover the pan or pot and reduce the heat to low—Cook for about 25 to 30 minutes, or until the lentils are tender**. Stir occasionally to make sure nothing sticks to the bottom.
Meanwhile, if you are serving this sauce with some pasta, bring a large pot of salted water to boil, add the pasta, and cook according to the package instructions.
Before serving, taste the sauce and adjust seasoning.
You can serve your pasta mixed with the sauce and let it rest for 5 minutes for better flavor. Or serve the pasta topped with the sauce.
Top with some vegan parmesan or parsley to serve (optional).