Step 1: Prepare the Cauliflower Steaks

1. Preheat your oven to 400°F (200°C). Line a baking sheet with parchment paper or lightly grease it with cooking spray.
2. Remove the outer leaves of the cauliflower and trim the stem slightly, leaving enough to hold the head together.
3. Slice the cauliflower vertically into 1-inch-thick slices. You should get about 4-6 steaks from one head. Reserve any small florets that break off for another use or roast them alongside the steaks.

Step 2: Season the Steaks

1. Arrange the cauliflower steaks on the prepared baking sheet. Drizzle both sides with olive oil and season with garlic powder, smoked paprika, thyme, salt, and black pepper.
2. Rub the seasonings into the cauliflower gently to ensure even coating.

Step 3: Roast the Cauliflower

1. Roast the seasoned cauliflower steaks in the preheated oven for 20 minutes. Flip the steaks carefully using a spatula halfway through to ensure even browning.

Step 4: Add the Cheese Topping

1. In a small bowl, mix the mozzarella, Parmesan, and cheddar cheeses.
2. Remove the cauliflower steaks from the oven and sprinkle the cheese mixture generously over each piece.
3. Return the steaks to the oven and roast for an additional 10-15 minutes, or until the cheese is melted, bubbly, and golden brown.

Step 5: Garnish and Serve

1. Transfer the cheesy cauliflower steaks to a serving platter and garnish with chopped parsley.
2. Serve immediately with your favorite sides or enjoy them as a standalone dish.