In a large bowl, add Spinach mixture, add Ricotta, Feta Cheese, Mozzarella Cheese and Parmesan Cheese. Mix well, until combined.
Brush Peppers with Olive Oil, sprinkle with salt. Fill each pepper with Spinach Cheese filling and top with Mozzarella Cheese.
Cover baking dish with foil paper and bake for 20 minutes, remove foil paper and bake for an additional 15 minutes, until peppers are tender, and cheese is golden brown. Remove from heat and ready to serve.