On medium-high heat, heat oil in a dutch oven or large deep skillet. Add sausage and cook until meat is browned, breaking up with meat chopper (or wooden spoon), about 5-7 minutes.
Add garlic and cook for 1 minute. Add tomatoes and Italian seasoning, and cook until sauce has thickened slightly, about 10 minutes.
Meanwhile, in a medium bowl, mix together ricotta, half of parmesan cheese, basil, egg, salt, and pepper.
Leave 1 cup of sauce in the bottom of the pot and put the rest of the sauce in a heat proof measuring cup or bowl. Spread sauce on the bottom of the dutch oven or skillet.
Cover sauce with a single layer of noodles, cutting to fit with scissors or a knife if needed.
Spread ⅓ of ricotta mixture, then a thin layer of sauce. Repeat twice.
On the final layer of noodles, cover with sauce. Cover with sliced mozzarella then sprinkle with remaining parmesan cheese. (See notes for layering details.)
Cover loosely with aluminum foil and bake 20 minutes. Remove foil and bake until bubbling and browned, about 20-25 minutes more. Rest for 10-15 minutes before serving.