Preheat oven to 350 degrees.
In a skillet cook the Italian sausage. Then add the onions and cook for a few minutes. Then add the sundried tomatoes. If you are trying to "hide them" from your kids chop them up if not slice into thin strips before adding. Then set aside.
In a bowl add the ricotta, mozzarella cheese, egg whisked, seasonings and the parmesan cheese. Mix together well.
In a 9x13 or (2) 9x9 pans add the marinara sauce. Then place the cooked jumbo shell pasta with the top open so that you can stuff them. Then take the cheese mixture and stuff each shell. Repeat until all the cheese filling is gone and the shells are all stuffed.
Then sprinkle the sausage and sun dried tomatoes on top. Then top with parmesan and/or more mozzarella cheese if you would like.
Bake for 25-30 minutes covered. Then serve