Preheat your oven to 425°F (220°C).

In a small pot or steamer, add water and bring to a boil. Add spinach for about 1 minute until wilted, chop finely, and set aside.

In a large pot, bring salted water to a boil, add large pasta shells, and cook for approximately 10 minutes until al dente. Drain and drizzle with olive oil.

In a mixing bowl, combine the chopped spinach, ricotta cheese, grated pecorino, minced garlic, oregano, lemon zest, red pepper flakes, salt, and pepper. Mix well.

Spread a layer of marinara sauce in a 9×13 baking dish. Stuff each pasta shell with the filling and arrange them in the dish, open side up.

Cover the dish with aluminum foil and bake for 20 minutes until the cheese is bubbling and edges are golden.

Let the dish cool for a few minutes before serving warm, drizzled with extra marinara sauce if desired.