01 - Preheat oven to 400°F. Line a baking dish with parchment paper or lightly grease it.
02 - Slice zucchini in half lengthwise and scoop out flesh, leaving a 1/4-inch thick shell. Finely chop the scooped flesh and set aside.
03 - Heat olive oil in a large skillet over medium heat. Add onion and diced red bell pepper, sauté 3 to 4 minutes until softened.
04 - Add minced garlic and chopped zucchini flesh to the skillet. Cook for 2 to 3 minutes, stirring occasionally.
05 - Stir in shredded chicken, tomato sauce, dried Italian herbs, salt, and black pepper. Cook for 2 minutes until thoroughly heated and combined.
06 - Remove skillet from heat and stir in half of the mozzarella cheese until blended.
07 - Arrange zucchini halves in the prepared baking dish, then evenly spoon the chicken mixture into each zucchini shell.
08 - Sprinkle remaining mozzarella and Parmesan cheese over the filled zucchini halves.
09 - Bake in preheated oven for 20 to 25 minutes, until zucchini is tender and cheese is melted and golden brown.
10 - Optionally garnish with chopped fresh basil or parsley before serving.