01 - Preheat oven to 425°F. Line a baking sheet with parchment paper.
02 - Remove leaves and trim stem from each cauliflower head. Slice into 3/4-inch thick steaks, yielding 2 to 3 steaks per head. Reserve loose florets for another use.
03 - Arrange cauliflower steaks on the prepared baking sheet. Brush both sides generously with olive oil and melted butter.
04 - Sprinkle each steak with garlic powder, smoked paprika, salt, and black pepper.
05 - Roast in the oven for 20 minutes, flipping once halfway through, until golden and tender.
06 - In a mixing bowl, combine mozzarella, cheddar, and Parmesan cheeses.
07 - Remove baking sheet from oven. Sprinkle an even layer of cheese mixture over each cauliflower steak.
08 - Return baking sheet to oven. Bake for 8 to 10 minutes, or until cheese is melted, golden, and bubbling.
09 - Sprinkle with chopped parsley immediately before serving, if desired.