Place shrimp in buttermilk and let rest 15 min. Combine cornstarch with salt, pepper, garlic powder and cayenne (optional). Heat oil in deep skillet until shimmering. Dip shrimp a few, at a time, into cornstarch mixture, shaking off excess and gently lower into oil (do not crowd pan). Fry, turn and cook until golden on both sides, approx. 4 min total. Repeat with remaining shrimp. Combine mayo, chili sauce, Sriracha and lime juice. Toss shrimp with sauce and serve with chopped cabbage and pepper slaw and rice with green onions sprinkled on top.
For Keto: Sub coconut flour for cornstarch, omit sweet chili sauce; up hot sauce to 3 T, to taste, and use a keto sweetener, to taste; sauce should be sweet, spicy and tart.