1. Fill a small bowl halfway with water and add ice cubes. Add onion slices and let soak for 5 minutes. Drain and pat dry. Transfer to a medium bowl with mango, radishes, and cilantro. Transfer salad mixture to refrigerator and let chill while preparing fish.

2. Fill a countertop electric fryer or deep pot 2 inches high with oil and heat to 350 degrees.

3. In a shallow dish, mix together flour and cornstarch and season with salt and pepper. Lightly dredge fish in flour mixture, shaking off excess. Working in batches, place the fish into a fryer basket or spider strainer and carefully lower into hot oil. Fry for 2 to 3 minutes, until golden brown and crisp. Transfer to a paper towel-lined plate; immediately season with salt and pepper.

4. Remove salad from refrigerator and drizzle with vinaigrette; toss to combine. Arrange on a serving platter and top with fish; serve immediately.