Cover the cashews with boiling water and let them soak for 15 minutes while you start the soup.
Heat the olive oil in a large Dutch oven over medium-high heat. Add the sausage and cook for 6 to 8 minutes, breaking it up, until browned. Add the onion and cook for 5 minutes until soft.
Stir in the garlic, oregano, dried basil, red pepper flakes and tomato paste and cook for 2 minutes until the paste darkens slightly. Add the crushed tomatoes and broth, bring to a boil, then simmer for 15 minutes.
Drain the cashews and add them to a food processor with the water, lemon juice, nutritional yeast, garlic and salt. Pulse and scrape down the sides until creamy but still slightly textured, just like ricotta.
Add the lasagna noodles to the simmering soup and cook for 10 to 12 minutes, stirring often so they don't stick, until tender. Season with the salt and pepper and stir in the fresh basil.
Ladle the soup into bowls and top each one with a generous spoonful of cashew ricotta. Serve right away, since the noodles keep soaking up broth as it sits.