Preheat the oven: Preheat the oven to 210°C (410°F).
Cut the cauliflower into steaks: Cut off the outer green leaves and trim off the bottom of the cauliflower stem. Make sure your slices are thick enough so that they won't fall apart. With a large knife, cut the cauliflower lengthwise through the center into thick pieces. Depending on the thickness of your cauliflower you will end up with 3-4 cauliflower steaks.
Prepare and season the cauliflower steaks: Transfer the cauliflower steaks to a baking tray and evenly sprinkle the seasonings (nutritional yeast, salt, pepper, onion and garlic powder) onto the cauliflower. Drizzle on the lemon juice and olive oil. Repeat those steps for the other side of the cauliflower. Make sure that both sides are evenly coated with spices, lemon juice and olive oil.
Bake: Bake the cauliflower steaks for about 25-30 minutes or until crispy and golden brown. Flip the cauliflower steaks after 15-20 minutes.
Serve: Transfer to a platter and garnish them with fresh thyme. Enjoy!