Make the avocado crema per link's instructions. Place in the fridge until ready to use.
Make the batter: mix the flour, salt, pepper, garlic powder, and cayenne pepper in a large bowl. Gradually whisk in the beer, until no lumps are formed. Let rest for 15 minutes.
Meanwhile, make the green cabbage slaw: toss shredded green cabbage, lime juice, cilantro, salt, and pepper. Set aside.
Heat oil in a 3 quart Dutch oven to cover about 2 inches of the pot. Using a candy thermometer, heat oil to 350 degrees F.
Season fish with cumin, salt, and pepper. Dredge fish in flour, shaking off any excess flour. Working in batches, dip each piece of fish into the beer batter. Deep-fry in the hot oil (350 degrees F) for about 5 minutes, or until golden brown and cooked through, turning occasionally. Transfer to a plate lined with paper towel to drain excess oil.
To assemble the tacos: Heat tortillas on open flame or microwave (see notes under Kitchen Tips). Double-up each tortilla. Place fish on tortillas. Top with the green cabbage slaw, tomatoes, cilantro, avocado slices. Drizzle with the avocado crema.
Serve immediately. Serve with lime wedges.