Combine ricotta & egg, season with sea salt and pepper. Set aside.
In a large (oven proof) skillet* fry your hot sausage over medium heat. (if your sausage is in links, remove outer casing and crumble)
Once your sausage is cooked through, add coconut oil if there isn't at least 2 tablespoons of fat from the sausage in the pan already. Then add he mushrooms, onions and garlic, cook over medium/low heat for about 3-5 minutes or until mushrooms are cooked and onions are soft.
Add tomato sauce and basil
Season your meat sauce with sea salt and pepper, to taste.
Add in thinly sliced zucchini and gently fold in. Add dollops of ricotta cheese and then top with mozzarella & parmesan cheeses (don't stir)
Broil for until the cheese is melted and starting to brown (5-10 minutes). Remove from the oven and allow to rest uncovered for 10-15 minutes prior to serving.
I recommend using a stainless or enameled cast iron pan. It's not ideal to use standard cast iron for cooking acidic foods like tomatoes.