First, have two 8 or 9” baking dishes ready—one is for dinner tonight, one is for the freezer.
Bring plenty of salted water to a boil, and cook the pasta shells 1 minute less than the package directions. Drain, toss lightly with olive oil, and set aside.
Preheat the oven to 350º F.
Next, defrost the spinach in the microwave according to the package directions. Remove the spinach from the bag, drain it, and use your hands to squeeze it dry. Try to remove as much of the moisture from the spinach as possible.
Place the spinach in a large bowl, and stir in the chicken, ricotta, and eggs. Mix very well. Stir in half of the grated Blarney Castle cheese. Add a big pinch of salt and some freshly grated black pepper.
Pour 1 cup of the Marinara in the bottom of each baking dish.
Once the shells have slightly cooled, remove a shell. Place it in the palm of your hand, and then squeeze your hand slightly closed to open up the shell for stuffing (see photo for reference).
Place a heaping tablespoon of filling in each shell, and then place each shell facing down in a baking dish. You should get about 10 shells in each dish.
Pour the rest of the Marinara on top of the shells, and sprinkle the remaining Blarney Castle cheese on top.
Cover one pan with freezer foil, and place it in the freezer for cooking at a later date. When ready to cook, defrost in the fridge overnight or place in a 200-degree F oven for 2 hours to slowly defrost and cook.
Slide the other pan in the oven, and bake until the sauce bubbling and the cheese is melted, about 20 minutes.