Preheat your oven to 375°F and lightly grease a small baking dish.
Cook the jumbo pasta shells in a large pot of boiling salted water until al dente, then drain and set aside to cool.
In a non-stick skillet over medium heat, brown the ground turkey with minced garlic, dried oregano, sea salt, and black pepper until fully cooked.
Pour the marinara sauce into the skillet with the turkey and simmer on low for 5 minutes to meld the flavors.
Steam the baby spinach until wilted, then squeeze out all excess moisture using a clean kitchen towel and finely chop.
In a medium bowl, combine the chopped spinach with the ricotta cheese until smooth.
Spoon a small amount of the turkey marinara sauce into the bottom of the prepared baking dish.
Fill each cooked pasta shell generously with the spinach-ricotta mixture and place them in the dish.
Top the shells with the remaining turkey marinara sauce and sprinkle with parmesan cheese.
Bake for 15 to 20 minutes until the sauce is bubbling and the cheese is lightly browned.