Heat the oven to 350°F and lightly grease a 9x13-inch baking dish with olive oil.
Cut the cauliflower head in quarters. Slice away the leaves and stem, and with an angled cut cut away the core from each quarter of the cauliflower head. Chop cauliflower roughly into bite-sized florets, each about 1-inch across.
Bring 3 quarts of water to a boil over high heat. Stir in the salt. Add the cauliflower florets and boil for 2 minutes. Drain into a colander set in the sink. Run cold water over the florets to stop the cooking process and shake the colander to drain any excess water. Return the cauliflower to the cooking pot and set aside.
Place a 10-inch sauté pan over medium-high heat. Add the olive oil and then, when the pan is quite hot, add the sausage. Use a spoon to break up the meat. Cook for 8 to 12 minutes, or until the sausage is cooked through and beginning to get crispy. If using chicken sausage there should not be a great deal of fat in the pan, but if using Italian sausage, drain all but 1 to 2 tablespoons of fat.
Turn the heat to medium-low and add the onion, garlic, and thyme to the pan with the sausage. Sauté for 5 to 6 minutes, stirring frequently. Scrape up any brown bits as you sauté. Crush the tomatoes, and add them to the sausage. Stir thoroughly, then add the reserved tomato sauce and cook for about 5 more minutes. Turn off the heat and taste the sauce. Add salt and pepper to taste.
Toss the sauce with the cauliflower in the cooking pot. Spread the cauliflower and sausage mix in the prepared baking dish and distribute evenly. Mix the bread crumbs and Parmesan and sprinkle them evenly over the cauliflower. Drizzle lightly with olive oil.
Place in the middle of the oven and bake for 25 minutes or until breadcrumbs have browned and the sauce is bubbling. Let stand for 5 minutes before serving.original recipe