Heat avocado oil in a Dutch oven or large pot over medium-high heat.
Add onion and cook 3 minutesstirring occasionally.
Add Italian sausage and cook another 3-5 minutesor until browned. (I use a meat chopper to keep it from clumping.)
Add minced garlic and cook one additional minute until fragrant.
Stir in tomato paste until heated through and thoroughly mixed.
Use 1/2 cup of the chicken broth to deglaze the pan.
Add remaining chicken brothtomatoes, oregano, crushed red pepper and bay leaves.
Bring to a boilreduce heat and simmer, covered, for 20 minutes.
Check the consistency of your soup. If it's too runny for your tastesimmer a few more minutes uncovered. (Mine turned out perfectly.)
Turn heat to low.
Stir in the mozzarella and parmesan cheeses until melted.
Add salt and pepper to taste if desired.I didn't. This will depend on the sodium content of your chicken broth and how spicy you want your soup.
Serve with some additional garnishesnot included in Nutrition Facts such as a dollop of ricotta cheese, additional grated parmesan and/or mozzarella, fresh oregano, parsley or basil.