01 - Preheat the oven to 375°F. Prepare the bell peppers by slicing off the tops and removing the seeds and membranes. Lightly brush the insides with olive oil and set aside.
02 - Heat 1 tablespoon of olive oil in a large skillet over medium heat. Add the diced onion and sauté for 2 to 3 minutes until softened. Stir in the minced garlic and cook for 1 additional minute until fragrant.
03 - Add the chopped spinach to the skillet and cook, stirring occasionally, for about 2 minutes until fully wilted. Remove the skillet from heat and let the mixture cool slightly.
04 - 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. Stir until evenly incorporated.
05 - Divide the chicken Florentine filling evenly among the prepared bell peppers, packing the mixture gently into each one.
06 - Arrange the stuffed peppers upright in a baking dish. Spoon approximately 2 tablespoons of marinara sauce over each pepper, then sprinkle the remaining 1/4 cup mozzarella cheese on top. Pour 1/4 cup of water into the bottom of the dish to prevent sticking.
07 - Cover the dish loosely with aluminum foil and bake for 25 minutes. Remove the foil and continue baking for 10 more minutes until the cheese is golden and the peppers are tender.
08 - Remove from the oven and let the peppers rest for 5 minutes before serving. Pair with a simple arugula salad or crusty garlic bread if desired.