Pre-heat the oven to 350 degrees. Bring a large pot of water to boil for the pasta shells.
While the water is coming to a boil bring the marinara sauce to a simmer in a large skillet. Add the beef and contents of the seasoning pouch and simmer for 2 minutes, breaking up any larger pieces. Take off the heat and set aside.
When the water boils, salt generously, add the pasta shells and cook for 2 minutes less than the time indicated on the package. Drain and let cool till cool enough to handle.
In a large bowl combine the ricotta cheese, half the mozzarella, parmesan, eggs, spinach and salt and pepper. Transfer to a large pastry bag or ziploc bag and snip a large opening in the corner.
Spoon half the beef sauce into the bottom of a 9 x 13 baking dish - spread evenly.
Working with one shell at a time, pipe in some of the filling and place in your baking dish. Repeat till you've used all of the filling. Top with the remaining beef sauce and reserved mozzarella.
Bake till hot, 30 - 40 minutes (see Notes for do-ahead instructions). Turn the oven to broil and continue cooking till the cheese is golden brown and bubbling, watching carefully to avoid burning.
Remove from the oven, let sit for 5 minutes and sprinkle with the chopped parsley before serving.