Popcorn Chicken Po'Boys

Cut chicken into 1-inch pieces. In large bowl, stir together buttermilk, hot pepper sauce, 1 tbsp of the garlic powder and 1/2 tsp of the salt. Add chicken; toss to coat. Cover with plastic wrap and refrigerate for 15 minutes. (Make-ahead: Refrigerate for up to 1 day.) Meanwhile, in separate large bowl, whisk together flour, remaining garlic powder, remaining salt and the pepper. Using slotted spoon, remove chicken from buttermilk mixture, letting excess drip back into bowl; reserve marinade. Dredge chicken, a few pieces at a time, in flour mixture, shaking off excess. Dip in reserved marinade, letting excess drip off. Dredge chicken again in flour mixture, a few pieces at a time, shaking off excess. In deep-fryer, wok or Dutch oven, heat enough oil to come 3 inches up side over medium-high heat until deep-fryer thermometer reads 300°F.   Working in batches, fry chicken until golden brown, 3 to 4 minutes, reducing heat if chicken browns too quickly. Remove with slotted spoon; drain on rack set over paper towel–lined baking sheet. Slice rolls in half horizontally partway through. Scoop out middle, leaving 1-inch border on all sides. Spread each roll with mayonnaise (if using); layer with lettuce, chicken, tomato, pickles and red onion.