01 - Preheat the oven to 375°F (190°C).
02 - Cut the tops off the bell peppers and remove the seeds and membranes. Lightly brush the peppers with olive oil and set aside.
03 - Heat 1 tablespoon olive oil in a large skillet over medium heat. Add the diced onion and sauté for 2–3 minutes until softened. Add the minced garlic and cook for an additional 1 minute until fragrant.
04 - Add the chopped spinach to the skillet and cook, stirring occasionally, until wilted, about 2 minutes. Remove the skillet from heat and let cool slightly.
05 - In a large mixing bowl, combine the cooked chicken, spinach mixture, ricotta cheese, 1/2 cup mozzarella cheese, Parmesan cheese, dried Italian herbs, salt, and black pepper. Mix thoroughly until evenly combined.
06 - Fill each bell pepper evenly with the chicken Florentine mixture, pressing gently to pack the filling.
07 - Arrange the stuffed peppers upright in a baking dish. Spoon marinara sauce over each pepper and sprinkle with the remaining 1/4 cup mozzarella cheese.
08 - Pour about 1/4 cup water into the bottom of the baking dish to prevent the peppers from sticking.
09 - Cover the dish loosely with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for another 10 minutes until the cheese is golden and the peppers are tender.
10 - Remove from the oven and let the peppers cool slightly for 5 minutes before serving.