Preheat the oven to 375°F (190°C). Lightly grease a baking dish with olive oil.
Using a sharp knife, carefully cut a deep pocket into the side of each salmon fillet without slicing completely through.
Season the salmon with half of the Italian seasoning, along with some of the salt and black pepper.
Heat a small amount of olive oil in a large skillet over medium heat. Add the spinach and cook just until wilted.
Stir ¼ cup mozzarella and ¼ cup Parmesan into the spinach. Remove from the heat once the cheese begins to melt.
Divide the spinach and cheese mixture between the salmon fillets, gently filling each pocket. Arrange the stuffed fillets in the prepared baking dish.
Melt the butter in the same skillet over medium heat. Add the shrimp and minced garlic. Cook briefly until the shrimp turn pink and are nearly cooked through. Transfer the shrimp to a plate.
Pour the heavy cream into the skillet. Add the remaining mozzarella and Parmesan along with the paprika and remaining Italian seasoning. Simmer gently for about 3 minutes, stirring until smooth and creamy.
Arrange the shrimp over the stuffed salmon and spoon the cream sauce over the fillets.
Bake the Creamy Tuscan Shrimp Stuffed Salmon for 15–20 minutes, or until the salmon is cooked through and flakes easily and the sauce is hot and bubbling.
Sprinkle with fresh parsley and garnish with lemon slices before serving.