In a bowl, mix the shrimp, sugar, salt, and ½ tsp of the Cajun seasoning. Cover and refrigerate for about 2 hours.
Drain and cut pepperoncini in half lengthwise. Drain red pepper, cut into pieces.
Heat a couple of inches of oil in a wide pot over medium high heat.
In a large bowl, mix flour, cornstarch, icing sugar, and remaining Cajun seasoning. Add the pepperoncini, red pepper, and beer. Whisk into a smooth, creamy batter. Add shrimp to the batter, mix until well coated.
Add the shrimp, pepperoncini and red peppers to the oil one at a time. Ensure you remove any excess batter before frying.
Cook in one layer only and avoid any too many shrimp or the oil will cool and the batter becomes lumpy and sticky. Fry until golden brown, about 3 minutes.
Remove the shrimp and peppers with a slotted spoon, drain on a paper towel and season with salt.
If you’re doing more than one batch, make sure the oil is fully heated before frying another batch.