Preheat oven to 450 degrees F. Line a baking sheet with foil; set aside. Trim stem and leaves from cauliflower. In a 4- to 6-quart Dutch oven bring the water to boiling. Add the head of cauliflower; simmer, covered, for 15 minutes. Remove cauliflower.
Meanwhile, in a small bowl combine panko, Parmesan cheese, thyme, and garlic salt. Drizzle with melted butter; toss gently to combine.
Place the head of cauliflower on the prepared baking sheet. Coat with crumb mixture.
Bake for 10 to 15 minutes or just until cauliflower is tender and crumbs are golden. Cut into wedges. Serve with salad dressing.