warm corn tortilla, lime wedges, sliced avocado, chopped cilantro, and shredded red cabbage (for serving)
Special Equipment: A deep-fry thermometer.
Lightly season cod with salt and black pepper. Transfer to a wire rack set inside a rimmed baking sheet. Chill, uncovered, at least 1 hour or up to overnight (this air-dries the surface so the batter will adhere better to the fish).
Whisk flour, cornmeal, seasoned salt, paprika, baking powder, baking soda, in a medium bowl. Add beer, club soda and vinegar and whisk just until combined and no lumps remain.
Fit a large heavy pot with thermometer; pour in oil to a depth of 3". Heat over medium-high until thermometer registers 375°. Working in batches, dip fish into batter, allowing excess batter to drip back into bowl. Lower carefully into oil and fry until light golden brown and just cooked through, 3–4 minutes. Transfer to paper towels to drain.
Serve fried fish with tortillas, pico de gallo, hot sauce, pickled vegetables, limes, avocado, cilantro, and cabbage.