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 the flesh, leaving a 1/4-inch shell. Finely chop the reserved flesh.
03 - Heat olive oil in a large skillet over medium heat. Add onion and red bell pepper, cook 3-4 minutes until softened.
04 - Stir in garlic and chopped zucchini flesh; cook for 2-3 minutes.
05 - Add shredded chicken, tomato sauce, dried Italian herbs, salt, and black pepper. Cook 2 minutes until evenly heated and combined.
06 - Remove skillet from heat and stir in half of the mozzarella cheese.
07 - Place zucchini halves in baking dish and spoon chicken mixture evenly into each.
08 - Sprinkle remaining mozzarella and Parmesan cheese over stuffed zucchini.
09 - Bake for 20-25 minutes until zucchini is tender and cheese is melted and golden brown.
10 - Optionally garnish with chopped fresh basil or parsley before serving.