01 - Preheat the oven to 375°F. Lightly grease a baking dish large enough to hold the peppers upright.
02 - Bring a large pot of salted water to a boil. Add the prepared bell peppers and blanch for 3 minutes. Drain and set aside to cool.
03 - Heat olive oil in a skillet over medium heat. Add onion and sauté for 3–4 minutes until softened. Add garlic and cook for another 30 seconds until fragrant.
04 - Add chopped spinach to the skillet and sauté until wilted, about 2 minutes. Remove from heat and let the mixture cool slightly.
05 - In a large bowl, combine cooked chicken, sautéed onion, garlic, spinach, ricotta, Parmesan, 1/2 cup mozzarella, cream cheese, Italian herbs, salt, pepper, and red pepper flakes if using. Mix thoroughly until fully incorporated.
06 - Fill each bell pepper evenly with the chicken Florentine mixture. Place peppers upright in the prepared baking dish.
07 - Sprinkle the remaining 1/2 cup mozzarella cheese over the tops of each stuffed pepper.
08 - Bake for 30–35 minutes, until the peppers are tender and the cheese on top is golden and bubbly.
09 - Remove from the oven and let rest for 5 minutes before serving.