In a large Dutch oven over medium-high heat, cook the sausage, breaking the meat into 1/2-inch pieces, until lightly browned, about 5 minutes. Stir in the garlic and cook until fragrant, about 30 seconds. Add the tomato sauce, diced tomato (with the juice), oregano, salt, sugar, and pepper flakes. Bring the mixture to a boil. Reduce the heat to medium-low and simmer until slightly thickened, about 10 minutes.
Stir in the water, pasta, 1/4 cup basil, and increase the heat to high, and bring to a boil. Reduce heat to medium and simmer vigorously, stirring often, until the pasta is still very firm but starting to soften, 6 to 8 minutes. Meanwhile, adjust the oven rack 8 inches from the broiler element and heat the broiler.
Remove the pasta from the heat and stir in the spinach, 3/4 cup mozzarella, and 1/2 cup of Parmesan. Dollop the surface of the pasta evenly with the ricotta and then top with the remaining mozzarella and Parmesan.
Broil the ziti until the cheese is bubbling and beginning to brown, 5 to 7 minutes. Remove from the oven and let the dish cool for 10 minutes. Sprinkle with remaining 2 tablespoons of basil and serve.