Prepare pasta according to package instructions. Cook until al dente. Reserve 1 cup of pasta water.
Preheat oven to 375ºF
In a mixing bowl stir together the Ricotta cheese and egg. Add in the Spinach and season with cayenne pepper, nutmeg, lemon zest, salt, and pepper.
Fold in the cooked pasta to the cheese mixture. Add pasta water a little at a time if needed to loosen up the cheese. Add 3/4 cup of the Mozzarella cheese.
Pour the mixture into a 9 x 13-inch baking dish. Cover the pasta with the remaining Mozzarella and Parmesan cheeses.
Bake in the oven for 15-20 minutes, until cheese is melted and it's golden and bubbly. Allow to rest 5 minutes before serving.