01 - Preheat oven to 375°F. Slice the tops off the bell peppers and remove all seeds and membranes. Lightly brush the outside of each pepper with olive oil.
02 - Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the chopped spinach and sauté for 2 to 3 minutes until wilted. Set aside to cool slightly.
03 - In a large mixing bowl, combine the ricotta cheese, 1/4 cup of Parmesan, egg, sautéed spinach, minced garlic, basil, oregano, nutmeg if using, and salt and pepper to taste. Mix until well blended.
04 - Fill each bell pepper evenly with the ricotta mixture and arrange them upright in a baking dish.
05 - Spoon the tomato sauce around the base of the peppers in the baking dish.
06 - Sprinkle the stuffed peppers with the shredded mozzarella and the remaining 1/4 cup of Parmesan cheese.
07 - Cover the dish with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for 10 more minutes until the peppers are tender and the cheese is golden and bubbly.
08 - Allow the peppers to rest for 5 minutes before serving.