01 - Preheat the oven to 375°F and 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.
04 - Add spinach to the skillet and sauté until wilted, about 2 minutes. Remove from heat and let cool slightly.
05 - In a large bowl, combine cooked chicken, sautéed onion, garlic, spinach, ricotta cheese, Parmesan, 1/2 cup mozzarella cheese, cream cheese, Italian herbs, salt, pepper, and optional red pepper flakes. Mix well until fully incorporated.
06 - Stuff the chicken Florentine mixture evenly into each bell pepper. Place peppers upright in the prepared baking dish.
07 - Sprinkle the remaining mozzarella cheese over the tops of the stuffed peppers. Bake for 30-35 minutes, or until the peppers are tender and the cheese on top is golden and bubbly.
08 - Remove from oven and let cool for 5 minutes before serving.