Heat the olive oil in a large soup pot over medium heat. Add the onion and sliced mushrooms. Cook until starting to brown and liquid is mostly evaporated.
Add the sausage and the seasonings - Worcestershire sauce, Italian seasoning, garlic powder, salt and pepper and red pepper flakes. Cook, breaking up the sausage into small pieces, until the sausage is starting to brown.
Add the rotisserie chicken and chicken broth. Cook, stirring occasionally until the soup is simmering.
Stir in the pasta and cook according to package directions, until it is al dente.
Stir in the spinach, about half at a time until it has cooked and wilted into the soup.
Turn the heat to low and stir in the ricotta cheese, Parmesan cheese and lemon juice. Continue to stir and heat through until the ricotta is melted into the creamy broth. Taste, adjust seasonings if needed, and serve.