First, cook spaghetti or pasta of your choice according to the package instructions. The pasta will finish cooking before the sauce. When it has cooked, drain off the pasta water, and leave it on the side until the sauce is done.
Meanwhile, in a separate pot, heat some one calorie cooking spray. Finely dice onion, and sauté until they turn soft and translucent, about 5 minutes.
Add finely minced garlic and cook for another minute, then add finely diced mushroom and celery. Cook until the mushrooms have reduced in size, about 5 more minutes, stirring occasionally. Then, add all the dried herbs, and cook for another minute while stirring.
Drain a tin of cooked lentils, and rinse them thoroughly. Add to the pot, along with tomato passata, tomato puree, and some salt and pepper. Place the lid on top, and leave the sauce to cook for 5-10 minutes.
Add more salt and pepper to taste, then pour the drained pasta into the sauce. Allow the pasta to heat back up for a minute. Finally, serve the mushroom and lentil bolognese in pasta bowls.
Optionally, you can top the dish with grated parmesan or freshly ground black pepper.