Cook the pasta in salted water according to the package instructions. I like to get the pasta going when there is about 10 minutes of cook time left for the bolognese.
To a high-speed blender or food processor, add carrots and garlic and blend until finely chopped. Transfer to a large pot. Add mushrooms to the blender and blend to finely chop, scraping under the blade as needed (or chop by hand). Transfer to the pot.
Turn the heat to medium and add the olive oil and ½ teaspoon salt. Stir to combine and cook until vegetables have softened and water has evaporated, about 5-7 minutes, stirring occasionally. Stir in the red pepper flakes for about 30 seconds, if using.
Stir in the lentils and walnuts to coat. Then stir in the water, marinara, soy sauce, and remaining ¼ teaspoon salt. Bring to a boil over high heat, then reduce the heat to medium-low to maintain a rapid simmer (uncovered) for about 30 minutes or until the lentils are cooked through, stirring every 5-10 minutes or so.
To thicken the lentils, transfer about 1 cup to the high-speed blender and blend until smooth (letting the steam escape), then stir back into the pot. Turn off the heat and stir in the parmesan. Taste and season with more salt, if needed. If it seems too soup-y, simmer it for a bit longer or blend up more of the lentils. If it seems too thick, add a splash of water.
Add pasta to your bowl and scoop the bolognese on top. Sprinkle with plenty of parm, parsley (if using), black pepper, and a generous drizzle of good olive oil.