Preheat your oven to 375°F (190°C).
Cook the jumbo pasta shells in boiling salted water according to package directions 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 and dried oregano until cooked through and slightly crispy.
Steam the fresh baby spinach until wilted, squeeze out all excess moisture thoroughly, and finely chop.
In a medium mixing bowl, combine the cooked ground turkey, chopped spinach, part-skim ricotta, egg white, sea salt, and black pepper until well incorporated.
Spread half of the marinara sauce evenly across the bottom of a small oven-safe baking dish.
Carefully stuff each cooked pasta shell with a generous amount of the turkey and ricotta mixture and arrange them in the baking dish.
Spoon the remaining marinara sauce over the top of the shells.
Cover the dish with foil and bake for 20 minutes; remove the foil and bake for an additional 5-10 minutes until the sauce is thickened and bubbling.