01 - Preheat oven to 375°F. Lightly brush a large baking dish with olive oil.
02 - Cut each bell pepper in half lengthwise and remove all seeds and membranes. Arrange the pepper halves cut-side up in the prepared baking dish.
03 - Heat 1 tablespoon of olive oil in a skillet over medium heat. Add the chopped onion and minced garlic, sautéing until translucent, about 3 minutes. Add the spinach and cook until wilted. Remove from heat and let cool slightly.
04 - In a large mixing bowl, combine the ricotta cheese, Parmesan cheese, egg, basil, parsley, salt, and black pepper. Fold in the cooled spinach mixture until evenly incorporated.
05 - Spoon the ricotta filling evenly among the pepper halves, mounding it gently. Sprinkle shredded mozzarella over each stuffed pepper and drizzle with the remaining olive oil.
06 - Cover the baking dish tightly with aluminum foil and bake for 25 minutes.
07 - Remove the foil and continue baking for an additional 10 minutes, until the mozzarella is bubbly and golden on top.
08 - Remove from the oven and let the stuffed peppers rest for 5 minutes before serving.