Gather the ingredients.
Preheat the oven to 400 degrees F (175 degrees C). Spray a 13-x9-inch baking dish with cooking spray.
Cut zucchini in half lengthwise; cut off and discard stem ends. Using a spoon, scoop and scrape out pulp from center of each zucchini half, creating a 1/2-inch-thick shell. Measure out 3/4 cup zucchini pulp, and discard or reserve remaining pulp for another use. Arrange zucchini halves, cut side up, in prepared baking dish. Sprinkle evenly with Italian seasoning, black pepper, and 1/2 teaspoon of the salt.
Heat a large skillet over medium-high heat. Add Italian sausage; cook, stirring and breaking up with a spatula, until browned and crumbly, about 5 minutes. Stir in onion, garlic, crushed red pepper, the 3/4 cup zucchini pulp, and remaining 1/2 teaspoon salt; cook, stirring occasionally, until vegetables are softened and liquid is absorbed, about 5 minutes. Stir in marinara, and bring to a simmer over medium-high heat. Simmer, undisturbed, until slightly thickened, 3 to 5 minutes. Remove from heat.
Spoon about 1/2 cup pork mixture into each zucchini half; sprinkle evenly with mozzarella and Parmesan.
Bake in the preheated oven until zucchini is tender and cheese is melted and golden brown, 20 to 25 minutes. Sprinkle evenly with herbs; serve immediately.