Preheat oven to 200C. In a large pot, bring salted water to a boil. Partially cook the pasta shells according to the producer’s instructions. However, only cook for 75 percent of the recommended cooking time, as you want the pasta to be al dente.
Remove shells from the stovetop and drain. Then refresh the pasta by running cold water over the top.
Wash and dry the spinach before chopping it very finely. Tip spinach into a large bowl. Mix in the Ricottas and Grated Parmesan until well combined. Season with salt and pepper to taste.
Grease an ovenproof tray with olive oil. Using a spoon, heap mixture into the shells one-by-one. As shells are filled, place them snugly into the tray, open end facing up.
Spoon passata across the top of the dish, until shells are fully surrounded by sauce. Cover and bake for approximately 20 minutes, removing foil for final five minutes.
Let the shells rest for about five minutes prior to serving.