With a sharp knife, cut the cauliflower into half. Slice in the center from top to bottom. This way you will have two cauliflower steaks. Leave the large stem at the bottom as it helps to hold together the "steaks". Use the remaining cauliflower for another recipe such as cauliflower wings. Or just freeze them for another time.
In a bowl, combine the flour, the plant-based milk, the water, paprika powder and garlic powder. Stir until well combined. Dip the cauliflower steaks into the batter, so they’re completely coated.
Pour the panko breadcrumbs on a plate. You could also use other breadcrumbs, but the cauliflower burger will get a lot crispier when you use panko breadcrumbs. So I highly recommend using panko breadcrumbs.
Turn the cauliflower steaks in the panko breadcrumbs. They should be evenly covered.
Line a baking sheet with parchment paper and carefully put the cauliflower steaks on top. Preheat the oven to 350 °F and bake them for 25 minutes. Turn them halfway.
After baking, carefully coat the cauliflower steaks with the BBQ sauce. I used a silicone basting brush for that.
Put the cauliflower steaks back in the oven and bake again for 15 minutes (still at 350 °F).
Serve the cauliflower steaks on burger buns together with vegan mayonnaise, lettuce, tomato and red onion slices. So yummy!