When the pasta is done, you’ll use the boiling pasta water to wilt the spinach. To prepare, place the spinach leaves in the colander. Once the pasta is al dente, remove from the heat and pour over enough boiling water to fully wilt it. Place the pot back on the stove and use a spoon to remove the hot greens to a bowl, then drain the pasta into the colander. Return the pasta to the pan with a drizzle of olive oil to prevent sticking. Squeeze out all the water from the greens using a paper towel, then chop it roughly.
To make the filling, combine the chopped spinach with the ricotta, Mozzarella, pumpkin puree, chili powder, nutmeg, sage, salt, and several grinds of black pepper in a medium bowl. Taste, and adjust seasonings as desired. Then stir in the egg.
Spread the tomato sauce across the bottom of the 9 x 13 and 9 x 9 baking dishes. Fill each shell with the filling, then arrange them in a single layer in the baking dishes: 24 shells in the 9 x 13 and 15 in the 9 x 9.
Top each pan with shredded Pecorino or Parmesan cheese. Bake for about 20 minutes, until the cheese is melted and the filling is warm.