Preheat oven to 450°F.
Toss cauliflower, oil, marjoram, salt and pepper. Roast on a large rimmed baking sheet until starting to soften and brown on the bottom, 15 to 20 minutes.
Toss the cauliflower with vinegar and sprinkle with cheese.
Return to the oven and roast until the cheese is melted and any moisture has evaporated, 5 to 10 minutes more.