Toss the shredded purple cabbage with the cilantro, lime juice, olive oil, and a pinch of salt in a bowl. Set aside in the fridge to marinate while you prepare the fish.
In a separate small bowl, stir together the sour cream, lime juice, and hot sauce until smooth. Set the crema aside.
Whisk together the rice flour, cornstarch, garlic powder, smoked paprika, cumin, and salt in a large bowl. Pour in the cold sparkling water and whisk until you have a smooth, slightly thick batter.
Heat about 2 inches of oil in a large heavy-bottomed pot or deep skillet to 375 degrees F. Pat the cod strips very dry with paper towels, then dip each strip into the batter, letting the excess drip off. Carefully lower them into the hot oil.Fry in batches for 3 to 4 minutes per batch, turning once, until the fish is golden brown and crispy. Transfer to a wire rack.
Warm the corn tortillas in a dry skillet over medium heat for about 30 seconds per side until pliable and lightly charred.
Assemble the tacos by placing a couple of crispy fish strips in each warm tortilla. Top with the cabbage slaw, sliced avocado, and a drizzle of the lime crema. Serve with lime wedges on the side.