Preheat your oven to 180°C (350°F).
Cook the pasta shells in a large pot of salted boiling water until just al dente, about 8 minutes. Drain and set aside to cool slightly.
In a mixing bowl, combine ricotta, shredded mozzarella, chopped spinach, and hot sauce. Mix until smooth and creamy, feeling the cheese soften and blend together.
Using a spoon or piping bag, stuff each cooked shell generously with the cheese mixture, feeling the oozy filling as you fill each one.
Arrange the stuffed shells in a baking dish, then pour marinara sauce evenly over the top, covering all the shells. Sprinkle grated Parmesan cheese over the sauce.
Cover the dish with aluminum foil and bake for 25-30 minutes, until the sauce is bubbling around the edges and the cheese looks melted and slightly browned.
Remove from the oven and let rest for 5 minutes; this helps the flavors settle and makes serving easier.
Sprinkle additional Parmesan on top if desired, then serve hot, enjoying the bubbling, cheesy goodness with crispy edges and tender shells.