Whisk 1 cup flour, cornstarch, sugar and soda water together for tempura and let chill.
Heat peanut oil in deep-fryer or a large Dutch oven to 375°F.
In a shallow pie plate, add 1 cup flour and 1 tablespoon Cajun seasoning and mix well.
Season okra with 2 tablespoons Cajun seasoning. Dip okra in seasoned flour and then in tempura batter and place in oil, 1 at a time and fry until golden, about 4 minutes. Remove to a paper towel lined sheet tray. Season with salt.
Serve with Scallion Dipping Sauce.
Scallion Dipping Sauce:
In a medium sized bowl, whisk together all ingredients.