Cook pasta according to package directions. Drain and set aside. Meanwhile, cook sausage in a hot skillet over medium heat until golden brown on all sides. Add tomatoes, thyme and rosemary and simmer 5 minutes. Remove from heat. In a medium bowl, combine ricotta cheese, mozzarella cheese and garlic powder and mix well. Spoon 1/2 cup of the tomato sauce in the bottom of a 4-quart casserole dish. Top with half of the cooked ziti. Top with half of the cheese mixture. Top with 1 cup of the tomato sauce. Repeat layers (remaining ziti and remaining cheese mixture). Top with remaining tomato sauce. Sprinkle remaining mozzarella and parmesan cheese over top. Cover with foil and bake 30 minutes. Uncover and bake 15 more minutes, until cheese is golden and bubbly.