Preheat the oven to 375°F.

Cook the jumbo shells according to package directions but reduce the cooking time by 1-2 minutes. Drain and then rinse the shells with cold water until they're completely cool and then lightly drizzle with a little olive oil.

Drain the thawed spinach and squeeze out as much excess water as possible.

In a large skillet heat the olive oil over medium high heat. Then add in the onion, garlic, and red pepper flakes and sauté until softened and beginning to brown. Add in the drained spinach and cook for another 3 minutes. Remove from the heat and let cool slightly.

In a large bowl, combine the ricotta, egg, parmesan, salt, pepper, nutmeg, basil, and thyme. Then fold in the spinach mixture until fully incorporated. Set aside.

Pour about half of the tomato sauce into the bottom of a medium 2 quart baking dish. Set the rest aside.

Fill each jumbo pasta shell with about 2-3 tablespoons of the spinach ricotta mixture. Then arrange the filled shells in the baking dish.

Pour the remaining tomato sauce over top of the shells and sprinkle with shredded mozzarella cheese.

Bake at 375°F for 25-35 minutes or until the sauce is bubbly and the cheese is melted.

Remove from the oven and garnish with fresh pesto if desired. Serve immediately.

Store covered in the fridge for up to 5 days.