Whisk together mayonnaise, sour cream, lime juice, hot sauce, smoked paprika, garlic powder, and a pinch of salt in a small bowl until smooth. Taste and adjust the lime or hot sauce if needed. Place in the fridge until ready to use.
Make the slaw:
In a large bowl, combine green cabbage, red cabbage, carrots, and cilantro.
Add about half of the Baja sauce and toss until everything is lightly coated. Set the slaw aside.
Cook the battered shrimp:
Pat shrimp dry with paper towels. Prepare a bowl with cornstarch. Place the shrimp inside and toss until they are lightly coated. Shake off any excess and transfer the shrimp to a plate.
In another bowl, whisk together flour, baking powder, salt, smoked paprika, garlic powder, and black pepper.
Slowly add the sparkling water or beer, whisking until the batter is thin and smooth. You should get something similar to pancake batter.
Add enough oil to a skillet to come about ½ inch (1-1.5 cm) up the sides and heat over medium-high until it reaches 350°F (175°C). The oil is ready when a drop of batter sizzles right away.
Dip each shrimp into the batter, allow the excess to drip off, and place them in the hot oil.
Work in batches. Cook for 2-3 minutes, flipping once, until lightly golden and crisp.
Transfer to a paper towel-lined plate and repeat with the remaining shrimp.
Assemble and serve the tacos:
Warm tortillas in a dry pan until they are soft and lightly charred. Add some slaw, then the shrimp, a few slices of avocado, and finish with a drizzle of the remaining Baja sauce.
Sprinkle with crumbled cheese and add sliced jalapeños for more heat. Finish with extra cilantro and a squeeze of fresh lime juice.
Notes
Use a neutral oil with a high smoke point, such as vegetable, canola, or sunflower oil. Avoid olive oil, which has a lower smoke point and a stronger flavor.
Fry the shrimp in batches so the oil temperature stays high. Overcrowding the pan can cause the shrimp to steam instead of crisp.
Dry the shrimp well before coating with cornstarch - it helps the coating adhere and keeps splattering to a minimum.
If the Baja sauce is too thick, stir in 1-2 teaspoons of water at a time until it reaches a desirable consistency.
Store leftovers separately in airtight containers in the fridge. The shrimp will keep for up to 2 days, though they’re best fresh. The slaw is best within 1 day, as it will soften over time. The sauce will keep for up to 3 days.
Reheat the shrimp in a skillet over medium heat or in the oven until warmed through to help bring back some crispness. Avoid microwaving, as it will make them soft.