01 - Preheat your oven to 375°F with the rack positioned in the center.
02 - Slice each bell pepper in half lengthwise. Remove the seeds and white membranes, then arrange the peppers cut side up in a baking dish lightly coated with olive oil or cooking spray.
03 - Drizzle 1 tablespoon olive oil over the pepper halves and season lightly with a pinch of salt and pepper.
04 - In a large mixing bowl, combine the ricotta, Parmesan, mozzarella, beaten egg, minced garlic, chopped basil, parsley, oregano, lemon zest, remaining salt, black pepper, and red pepper flakes if using. Mix thoroughly until completely smooth and well incorporated.
05 - Spoon the ricotta mixture evenly into each pepper half, creating a slight mound on top. Use the back of the spoon to press the filling gently into the cavities.
06 - Drizzle the remaining 1 tablespoon olive oil over the stuffed peppers. If desired, sprinkle the extra Parmesan cheese over the tops for an additional golden crust.
07 - Cover the baking dish tightly with aluminum foil. Bake for 25 minutes until the peppers begin to soften.
08 - Remove the foil and continue baking for an additional 10 minutes, or until the peppers are completely tender when pierced with a fork and the cheese is golden and bubbly.
09 - Remove from the oven and let rest for 5 minutes. Garnish with fresh basil leaves before serving warm.