Cook pasta shells according to package instructions. Drain and set aside.
Heat olive oil in a pot over medium heat. Add chopped spinach and cook until it starts to wilt, about a minute, stirring constantly. Remove from heat and set aside.
Combine all sauce ingredients in a pot over medium heat. Bring to a light simmer while stirring together. Then pour the sauce into a 9x13 inch baking dish, spreading it out.
Combine smoked salmon, cooked spinach, ricotta cheese, and salt in a mixing bowl. Stir until well mixed. Use this mixture to generously stuff each pasta shell, and place the stuffed shells on top of the sauce in the baking dish.
Cover with foil and bake for 30 minutes at 350 F. Uncover and bake for another 5 minutes. Optionally, top with finely grated parmesan cheese.