Preheat oven to 425 degrees F. In a small bowl whisk together olive oil, mustard, caraway seeds, and salt. Spread caraway mixture over the cauliflower. Place water into an 8- to 10-inch cast iron or other oven-going skillet. Place cauliflower in skillet; cover with foil. Bake for 30 minutes. Meanwhile, in a small bowl combine the onion, vinegar, sugar, and salt; set aside, stirring occasionally.
Uncover cauliflower and increase oven temperature to 450 degrees F. Continue roasting, uncovered, 30 minutes more or until golden brown and tender. Serve with prepared pickled red onions, dried apricots, and, If desired, additional mustard and rye bread.