01 - Preheat oven to 425°F (220°C). Line a baking sheet with parchment paper.
02 - Remove leaves from cauliflower heads, trim the stems, and cut each into 3/4-inch thick steaks. Reserve any loose florets.
03 - Arrange cauliflower steaks on the prepared baking sheet and brush both sides with olive oil and melted butter.
04 - Sprinkle the steaks with garlic powder, smoked paprika, salt, and black pepper.
05 - Roast in the oven for 20 minutes, flipping the steaks halfway through, until golden and tender.
06 - In a bowl, combine mozzarella, cheddar, and Parmesan cheeses.
07 - Remove baking sheet from oven and top each cauliflower steak with a generous layer of the cheese mixture.
08 - Return to oven and bake for 8 to 10 minutes, or until the cheese turns golden, bubbly, and fully melted.
09 - Scatter chopped parsley over the steaks before serving, if desired.