The cheese is the primary ingredient that you will find in Italian cuisines and it never overrides the original taste of the recipe. That is how you balance the contents of a recipe correctly and Italian cuisine has mastered it.
Preheat the oven to 350oF. Brush a large rimmed baking sheet with some oil on it.
Take a large pot and boil some water in it with added salt. Cook rigatoni in this pot according to the instructions until it becomes soft.
Drain it and lay all of it on the prepared baking sheet.
Now, mix ricotta, spinach, egg, parmesan, garlic, and lemon zest in a large bowl. Add some salt and a pinch of red pepper flakes to it.
Shift this mixture to a piping bag or any resealable plastic bag and snip its one corner.
Add a layer of sauce into the bottom of a large skillet or baking dish. Stuff the rigatoni with ricotta mixture and keep it on top of sauce in concentric circles in a smooth layer.
Add more sauce and top it with some mozzarella and place another layer of filled rigatoni on the top of it.
Garnish with some parmesan and place the skillet in the oven. Bake it until the top feels crispy and the sauce begins to bubble. It would take you 30 minutes to bake it thoroughly and enjoy!