Preheat your oven to 175°C (350°F).
In a large pot, cook the pasta according to the package instructions. Drain and set aside.
In a large skillet, cook the chicken sausage slices over medium heat until browned. Remove from the skillet and set aside.
In the same skillet, add the butter and melt over medium heat. Add the flour and whisk continuously for 2 minutes to form a roux.
Gradually whisk in the milk, ensuring there are no lumps. Cook until the mixture thickens, about 5 minutes.
Stir in the shredded mozzarella cheese, grated Parmesan cheese, garlic powder, Italian seasoning, salt, and pepper. Continue to stir until the cheese is fully melted and the sauce is smooth.
In a large mixing bowl, combine the cooked pasta, chicken sausage, and sliced zucchini. Pour the cheese sauce over the mixture and stir until everything is evenly coated.
Transfer the mixture to a 9x13-inch baking dish, spreading it out evenly.
Bake in the preheated oven for 25-30 minutes, or until the casserole is bubbly and the top is slightly golden.
Remove from the oven and let it cool for a few minutes before serving.