Make the slaw: Combine cabbage, cilantro, lime juice, olive oil, and salt in a bowl. Chill in the fridge.
Make the sauce: Mix crema/sour cream, mayo, lime juice, garlic, and hot sauce. Set aside.
Prep the fish: Cut into strips and pat dry. Season with salt and pepper.
Heat oil: Add 2 inches of vegetable oil to a pan and heat to 350°F.
Prepare batter: Mix flour, baking powder, garlic powder, cumin, cayenne, salt, and pepper. Whisk in beer until smooth.
Fry the fish: Dip fish into batter, then fry for 2–3 minutes until golden. Drain on paper towels and season with salt.
Warm tortillas: Heat in dry pan for 30 seconds per side or in foil in the oven.
Assemble tacos: Add fish to tortillas, then top with slaw, sauce, avocado, cilantro, and lime juice. Serve immediately.