01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - Remove the leaves from each cauliflower head, trim the stem flat, and slice vertically into 3/4-inch thick steaks. Expect approximately 2 to 3 steaks per head; reserve any loose florets for another use.
03 - Place cauliflower steaks in a single layer on the prepared baking sheet. Brush generously with olive oil and melted butter on both sides.
04 - Sprinkle garlic powder, smoked paprika, salt, and black pepper evenly over both sides of each steak.
05 - Roast in the oven for 20 minutes, flipping once halfway through, until the cauliflower is golden and fork-tender.
06 - While the cauliflower roasts, combine mozzarella, cheddar, and Parmesan cheeses in a mixing bowl.
07 - Remove the baking sheet from the oven. Mound a generous layer of the cheese blend over each cauliflower steak.
08 - Return the baking sheet to the oven and bake for 8 to 10 additional minutes, or until the cheese is fully melted, golden, and bubbly.
09 - Transfer steaks to a serving platter. Scatter chopped fresh parsley over the top, if desired, and serve immediately.