In a large skillet with the heat set to medium, add enough oil to cover the bottom of the pan by 1 inch.
In a large bowl, combine flour, cornstarch, baking powder, salt, and garlic powder.
Toss the shrimp in your flour mixture, then skewer each shrimp (3 on each skewer) and set aside.
To your flour mixture, whisk in the can of soda water.
Coat each skewer in your wet flour mixture, then fry on each side until golden brown, about 2-3 minutes per side. Use a pair of tongs to flip your skewers.
For the boom boom sauce, combine all ingredients except sesame seeds and scallions in a medium-sized bowl.
Taste and adjust flavor as necessary. Serve on the side with scallions garnished on top of the sauce.