Make sure you have your potato skins ready to go. See notes for links to recipes for potato skin shells.
Cook the Italian sausage as per package directions until just cooked through. Slice into 1/4-1/2 inch coins and set aside.
Preheat oven to 350F.
Once your potato skins are prepared (see note below for recipe), place them skin side down on a large cookie sheet.
Sprinkle approximately 1/2 Tablespoon of mozzarella cheese in the bottom of each potato skin shell. Use just enough cheese to cover the bottom.
Spoon approximately 1 Tablespoon of marinara sauce into each potato skin shell. Top with another Tablespoon or so of mozzarella.
Sprinkle with Parmesan cheese and add cooked Italian sausage slices to the top of each potato skin. Sprinkle with a little dried oregano.
Bake until the cheese on top is starting to brown and the cheese filling is hot and starting to bubble, approximately 12-15 minutes. Serve immediately and with additional marinara sauce if desired.