Cut 1 large head cauliflower into bite-sized florets.
Pour the canola oil into a heavy-bottomed pot or deep fryer and heat it to 350°F.
Whisk the 1 cup all purpose flour, ½ cup cornstarch, 1 teaspoon garlic powder, 1 teaspoon fine sea salt, ½ teaspoon black pepper, and 1 teaspoon baking powder in a large bowl.
Pour in the 1¼ cups ice cold club soda or sparkling water and whisk just until the batter is smooth.
Add the cauliflower to the batter, let the excess drip off, then lower it into the hot oil in batches. Fry until golden and crisp, and the cauliflower is tender, about 4 to 5 minutes per batch. Transfer the pieces to the wire rack and repeat with the remaining cauliflower.
Add ½ cup Korean BBQ Sauce, ¼ cup honey, 2 tablespoons soy sauce, 2 tablespoons gochujang, and 1 teaspoon toasted sesame oil to a small saucepan. Cook over medium-low heat, stirring often, until slightly thickened, about 3 to 5 minutes.
Toss the fried cauliflower with just enough sauce to coat the outside without soaking it. Transfer to a serving platter and finish with thinly sliced green onions and white sesame seeds. Serve right away.