Bring a medium-large pot of water to a boil, add salt and pasta. Cook until pasta is al dente. Reserve 1/3 cup of the pasta water. Drain and set aside.
Heat a large 12 inch skillet or cast iron Dutch oven over medium-high heat. Add 2 tablespoons of olive oil and once warm, add mushrooms. Sauté for about 3-4 minutes, once water has evaporated and mushrooms are cooked, transfer to a bowl and set aside.
Add onions, cut carrots and celery to a food processor, pulse until they are finally chopped. Add to the same skillet or Dutch oven and add the remaining olive oil if needed. Sauté for 2 minutes, then add garlic, sauté for 1 minute.
Add vegetable broth into the skillet or Dutch oven, cook for 1 minute, then add tomato pasta and crushed tomatoes. Add oregano and basil. Season with salt and pepper. Simmer for 20 minutes. The last 5 minutes, add the 1/3 cup of reserved pasta water.
While the sauce to cooking, toast chopped walnuts in a small skillet over medium heat, for about 5 minutes. Long enough for them to start turning a golden colour. Add the toasted walnuts to the sauce.
Serve into bowls or rimmed plates and garnish with fresh herbs and few red chili flakes if desired. Enjoy!
