01 - Preheat oven to 425°F (218°C). Line a baking sheet with parchment paper.
02 - Remove leaves from cauliflower heads, trim stems, and cut each into 3/4-inch thick slices to create steaks; reserve loose florets for another use.
03 - Place cauliflower steaks 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 over both sides of the steaks.
05 - Roast in the oven for 20 minutes, turning halfway through, until golden and tender.
06 - In a mixing bowl, blend together mozzarella, cheddar, and Parmesan cheeses.
07 - Remove steaks from oven and generously sprinkle cheese mixture over each one.
08 - Return baking sheet to oven and bake for 8 to 10 minutes, or until the cheese topping is golden and bubbly.
09 - Sprinkle with chopped parsley just before serving, if desired.