In a large saucepan, boil water and cook the pasta as per packet instructions. Drain, then allow pasta shells to cool.
In a frying pan, splash some oil and bring up to heat. Fry off the chicken mince until half cooked, then add the sage and onion until softened.
Add Marsala, bring to the boil, add the spinach leaves then put a lid on to allow the spinach to wilt down. This will take around 5 minutes.
Turn off the heat. Empty frying pan into a large bowl and add in the ricotta and half of the Parmesan. Allow mixture to cool down, then add in the egg, season with salt and pepper and combine the mixture.
Fill all the conchiglioni with the chicken mixture. Place the filled pasta shells on a baking tray. Pour over the Napoli sauce and sprinkle with the remaining Parmesan cheese. Cover with foil.
Place into a pre- heated oven at 200C for 15 minutes.