PREHEAT your oven to 400 degrees Fahrenheit.
ADD ghee or coconut oil to a large stockpot or Dutch oven and bring to medium heat. Add onion and garlic and sauté until it begins to soften, about 3 minutes.
ADD sausage and break up well with a wooden spoon. Season with sea salt and pepper and cook with the onion until it is cooked through and has browned a bit, about 10 minutes. Turn the heat off and stir in marinara sauce and tomato paste. Transfer to an ovenproof baking dish.
ARRANGE sliced zucchini in the sausage mixture by allowing thirds of the zucchini to stay above the mixture so that they brown a bit when baked. Transfer to your oven and bake, uncovered, until the zucchini is soft and browned, about 30 minutes.
SERVE between 4, garnishing with optional fresh parsley, storing any leftovers in a glass container in the fridge for 3 days.