Place the oil in a deep pot or dutch oven and heat to 365-370°F.
Rinse and pat dry the cod fillets. Season lightly with salt and black pepper on all sides. Set aside.
In a shallow bowl, whisk together flour, cornstarch, baking powder, seafood seasoning, seasoned salt, paprika, garlic and onion powders. Remove ⅓ cup to a separate shallow dish.
Whisk egg and beer into remaining dry ingredients until fully combined to form batter.
Dip the coated cod fillet first into the reserved dry ingredients then into the batter allowing any excess to drip off. Carefully lower into the oil.
Cook in batches for 6-8 minutes total, turning as needed until deep golden brown. Have nearby a pan lined with paper towels to drain. Season lightly with additional seasoned salt immediately upon removing from oil.
To assemble: Place 2 pieces of fish on each tortilla. Top with shredded savoy cabbage or lettuce, drizzle with cilantro lime crema. Top with tomatoes, avocado, jalapeno slices, red onion and queso fresco OR any of your favorite taco fixins'.
To make Crema: In a mixing bowl, whisk together crema, lime juice, mayonnaise, cilantro, garlic salt and onion powder. Cover and keep chilled until serving. This can be done up to one day in advance.