Preheat the oven to 450ºF.
*Breadcrumbs: If you are using gluten-free crackers or cornflakes, pulse them in a food processor until coarsely ground. Or use store-bought panko.
Make the batter: In a large bowl, mix the flour, cornstarch, chili garlic sauce, garlic powder, onion powder, salt, and pepper. Add the lemon juice. Gradually add the milk until you have a smooth batter that's thick enough to coat the back of a spoon. Add more milk as needed if the batter is too thick.
Coat florets: Place the breadcrumbs in a large bowl beside the batter bowl. Transfer the florets to the batter bowl and use a silicone spatula to toss them until evenly coated. Then transfer them to the breadcrumbs, a few at a time, and toss with a clean spatula to coat evenly.
Bake: Place the florets on a large nonstick or lined baking sheet in a single layer. Make sure they are not touching. Bake for 25 minutes, or until they are lightly crispy and golden brown.
Make the bang bang sauce: Meanwhile, in a large bowl, mix the vegan mayonnaise, chili garlic sauce, and maple syrup until combined.
Toss the baked cauliflower in the sauce using a silicone spatula until evenly coated. Place them back onto the baking sheet and bake for 2 to 3 minutes more, or until the sauce just starts to gently bubble.