Preheat the oven to 375 F or 200 C.
Boil the jumbo shells according to package instructions- then drain and keep ready.
In a small saucepan, sauté ½ of the crushed garlic in olive oil.
When it is fragrant, add the chopped tomatoes and passata. Simmer for 15 minutes covered.
Season with salt, pepper, basil, oregano and ½ the chilli flakes and set aside.
In the meantime, sauté the rest of the garlic and the onion in some olive oil. When the onions are translucent, add the spinach and cook until it has wilted. Turn off the heat and let it cool.
In a medium sized bowl, combine the ricotta, egg, nutmeg and remaining chilli flakes. Whisk until smooth.
Add in the feta and parmesan and season with salt and pepper according to taste.
Finally, add the spinach and onion mixture and gently incorporate.
Grease a dish with olive oil. Spread ½ of the sauce on the bottom.
Take each shell and fill with around 2 tbsp of the mixture. Arrange mixture-side up on the sauce.
Cover all the shells with the remaining sauce.
Cover the pan with aluminium foil and bake for 20 minutes. Then uncover and bake for 10 more minutes.
Sprinkle with more parmesan before serving.