01 - Preheat oven to 425°F. Line a baking sheet with parchment paper and set aside.
02 - Remove the leaves from each cauliflower head and trim the stem flush. Standing the head upright, slice vertically into 3/4-inch thick steaks. You should get 2 to 3 steaks per head. Reserve any loose florets for another use.
03 - Place the cauliflower steaks in a single layer on the prepared baking sheet. Brush both sides generously with olive oil and melted butter.
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 the steaks once halfway through, until golden and fork-tender.
06 - While the cauliflower roasts, combine mozzarella, cheddar, and Parmesan cheeses in a mixing bowl. Toss to distribute evenly.
07 - Remove the baking sheet from the oven. Pile a generous, even layer of the cheese blend over each cauliflower steak.
08 - Return the baking sheet to the oven and bake for 8 to 10 more minutes, until the cheese is fully melted, golden, and bubbling.
09 - Transfer the steaks to a serving platter and garnish with chopped fresh parsley if desired. Serve immediately.