Preheat oven to 375°.
Preheat a skillet over medium heat. When pan is hot, throw in sausage. Cook til just about done.
Add onions, zucchini, Italian seasonings, salt, and pepper. Cook about 7 minutes, until the zucchini starts to get tender and some juices release.
Lower the heat to medium-low and add in the heavy cream and tomato paste. Mix thoroughly and coat the veggies. Cook for about 3 minutes. The juice in the pan will start to thicken up a bit. Take off the heat.
In a separate bowl thoroughly mix the ricotta with the egg and add a pinch of salt.
Time to layer it up!
To a 9×5 casserole dish, add a thin layer of the zucchini/sausage mix. Add a layer of the ricotta. Repeat your layers, finishing with the zucchini as the last layer. Top with the shredded mozzarella, and cover the dish with foil.
Bake for 45 minutes. Take off the foil and cook for 10-15 minutes more until the cheese is melty and browned.