Crumble the sausage and add it to a skillet on medium high heat. Cook through and drain any excess renderings. Add the black pepper, onion powder, granulated garlic, and oregano.
Reduce the medium heat and add the sauce and bring it to a simmer, then gently stir in the tortellini
Thoroughly stir in the Parmesan cheese and half of the mozzarella cheese.
Taste for salt and add as needed for taste.
Sprinkle the remaining mozzarella over the top of the tortellini with sausage.
Cover with foil and place the skillet in the oven. Bake for 25 minutes.
When time is up, remove the foil and bake for 5 more minutes, or until the cheese is bubbling and melted.
Notes
Don't boil the tortellini separately. Cooking it directly in the sauce gives you better flavor and one fewer pot to wash. The starch from the pasta thickens the sauce naturally.
Shred your own cheese. Pre-shredded mozzarella contains anti-clumping agents (cellulose) that prevent the smooth, stretchy melt you want for the baked topping.
Reserve some mozzarella for the top. Stirring part of the cheese into the pasta and saving the rest for the top gives you two textures: creamy inside, bubbly and golden on top.
Use a cast iron skillet. Cast iron holds heat evenly, which is why the baked cheese melts so consistently. It also goes from stovetop to oven without swapping pans.
Watch the salt. Italian sausage, marinara sauce, and Parmesan all bring sodium. Taste before adding salt and adjust at the end.