Heat broiler, with rack in highest position. Pat fish dry with paper towels and gently coat with oil on a rimmed baking sheet. Season with salt and pepper. Broil until fish is browned on top and flesh is opaque throughout, 5 minutes.
Meanwhile, in a small bowl, combine sour cream, lime zest and juice, and a few dashes hot sauce. Season with salt and pepper. Toast corn tortillas over a kitchen burner using tongs or wrap in parchment-lined foil and heat in oven, 5 minutes. Divide fish evenly among tortillas and top with cabbage, cilantro, and onion. Serve with lime sour cream and lime wedges.
