01 - Preheat the oven to 375°F.
02 - Cut the tops off the bell peppers and remove all seeds and membranes. Lightly brush the insides with olive oil and set aside.
03 - 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. Add the minced garlic and cook for 1 additional 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.
05 - In a large mixing bowl, combine the cooked chicken, sautéed spinach mixture, ricotta cheese, 1/2 cup mozzarella cheese, Parmesan cheese, dried Italian herbs, salt, and black pepper. Mix thoroughly until evenly incorporated.
06 - Divide the chicken Florentine filling evenly among the prepared bell peppers, packing each one generously.
07 - Arrange the stuffed peppers upright in a baking dish. Spoon marinara sauce over the top of each pepper, then sprinkle with the remaining mozzarella cheese. Pour approximately 1/4 cup of water into the bottom of the dish to prevent sticking.
08 - Cover the dish loosely with aluminum foil and bake for 25 minutes.
09 - Remove the foil and continue baking for 10 minutes until the cheese is golden and bubbly and the peppers are tender. Let rest for a few minutes before serving.