Melt fat in a large skillet, Dutch oven, or stock pot. Sauté onions until very soft and brownish. Add the garlic and cabbage. It will look like a lot of cabbage, but it will cook down! Cover and continue to cook, stirring occasionally, until cabbage is also very soft. If it starts to stick, add a tablespoon of water and cover.
When the cabbage mixture is soft, season with salt and pepper to taste and spread in a baking dish, such as a 9x13" pan.
Preheat oven to 350° F.
In a dry skillet, toast the fennel seeds if using. Spread them in the hot skillet for 2-3 minutes. When they are a little bit brown and smell fragrant, they are ready.
Add all the pork to the skillet and break it up so it browns in crumbly pieces. While it cooks, add the Italian seasoning and garlic or garlic powder. When the meat is cooked, add salt and pepper to taste. Spread it over the cabbage in the baking dish.
Spread the pasta sauce over the top of the sausage. Sprinkle with cheese and bake at 350° F until the cheese is melted and bubbly. Cool before serving.