In a medium bowl, soak the shrimp in buttermilk for at least 30 minutes to tenderize and flavor them.
In a separate bowl, combine flour, garlic powder, paprika, cayenne pepper, salt, and black pepper.
Remove shrimp from buttermilk, allowing excess to drip off. Dredge each shrimp in the flour mixture, shaking off any excess.
Dip the coated shrimp into the panko breadcrumbs, pressing gently to adhere.
Heat about 1 inch of oil in a large skillet over medium-high heat. Once hot, fry the shrimp in batches for 2-3 minutes on each side until golden brown and crispy. Drain on paper towels.
In a small bowl, mix together mayonnaise, sweet chili sauce, and sriracha. Adjust the spiciness to your liking.
To assemble the tacos, warm the corn tortillas in a dry skillet or microwave. Layer with shredded cabbage, crispy shrimp, avocado slices, and drizzle with the bang bang sauce.
Serve with lime wedges on the side for squeezing over the tacos.