Preheat the oven to 400°F/200°C. Line a large rimmed baking sheet with parchment paper.

Remove the outer leaves from the cauliflower and trim the stem, keeping the head intact. Slice the cauliflower into 1/2-inch/1.25 cm thick slabs, letting any smaller florets fall away naturally.

In a medium bowl, whisk together the olive oil, Parmesan, garlic, paprika, salt, and pepper. Arrange the cauliflower in a single layer on the prepared baking sheet, then brush or spoon the mixture generously over both sides of each slice and floret.

Roast for 20 to 25 minutes, flipping halfway through, until the edges are deeply golden and the stems are tender when pierced with a knife.

Remove from the oven and sprinkle the mozzarella evenly over the cauliflower. Return to the oven and roast for another 5 to 7 minutes, or until the cheese is fully melted and beginning to brown in spots.

Transfer to a serving platter. Sprinkle with parsley, if using, and serve hot or warm.