Begin by preheating your oven to 425°F. Meanwhile, prepare the spinach by placing it in a steamer basket set over a pot containing about 1 inch of water. Heat the water until it simmers, then cover and steam the spinach for about 1 minute, just until it wilts. Remove the spinach and press out any excess moisture, then chop it finely.

Next, bring a large pot of salted water to a boil and cook the pasta shells for about 10 minutes, or until they reach an al dente texture. Drain the shells thoroughly, then drizzle them with a touch of olive oil to prevent sticking.

In a medium-sized mixing bowl, combine the chopped spinach with the ricotta cheese, grated pecorino, garlic, oregano, lemon zest, red pepper flakes, and ¾ teaspoon of sea salt. Add several grinds of black pepper, then mix everything until the filling is well-blended.

Take a 9x13 inch baking dish and spread a generous layer of marinara sauce across the bottom. Carefully fill each pasta shell with the spinach and cheese mixture, then arrange them in the baking dish. Cover the dish with foil and bake for 20 minutes.

Serve the stuffed shells hot, accompanied by additional marinara sauce on the side. Finish by sprinkling extra pecorino cheese over the top for added flavor.