Preheat your oven to 200℃ and line a baking sheet with baking paper.
In a large bowl, combine flour, cornstarch, garlic powder, onion powder, baking powder, paprika, salt, and black pepper until well mixed. Pour in the milk and whisk everything together until smooth.
Add the washed cauliflower into the batter and toss until each piece is well coated. Sprinkle in the panko breadcrumbs and toss again until they're evenly distributed.
Spread the battered cauliflower out on your prepared baking sheet in a single layer. Bake for about 20–22 minutes or until they are golden brown and crispy.
In a medium bowl, mix together mayonnaise, sweet chili sauce, sriracha, and rice vinegar (if using). Stir well until fully combined.
Once your cauliflower is done baking, remove it from the oven and transfer it back into the mixing bowl. Pour over your prepared bang bang sauce and toss everything together until each piece is evenly coated.