Preheat oven to 400ºF. Remove the plastic lid and top the stuffed shells with the basil marinara. If the marinara is still frozen, place in a bowl of hot water while the oven preheats. Cover with foil and place in the preheated oven for 20 minutes.
Now remove the pan from the oven and sprinkle the mozzarella cheese and buttered parmesan breadcrumbs on top of the shells. Return to the oven, uncovered, for an additional 20-25 minutes. It is recommended to cook the shells to an internal temperature of 165ºF.