Combine flour, cornstarch, baking powder, salt, garlic powder, and cayenne pepper in a bowl. Stir in beer and egg.
Mix mayonnaise, chipotle peppers, adobo sauce, and lime juice together in a bowl.
Heat oil in a deep-fryer or large saucepan to 375 degrees F (190 degrees C).
Coat cod pieces in 1/3 cup flour until completely covered. Shake off excess flour; dip into beer batter. Cook cod in oil a few pieces at a time until batter turns a golden brown color, 4 to 5 minutes. Remove from oil and place on paper towels to drain oil excess. Sprinkle with salt.
Place fried cod pieces on tortillas. Top with lettuce, queso fresco, tomato, red onion, cilantro, and chipotle-lime sauce. Serve with lime wedges.
