Heat oven to 400° F. In a small bowl, combine the avocado, apple, onion, jalapeño, cilantro, 1 tablespoon lime juice, and ½ teaspoon salt. Set aside.
Heat the oil in a skillet over medium heat.
Season the cod with ½ teaspoon salt and ¼ teaspoon pepper. Cook until opaque throughout, 3 to 5 minutes per side.
Meanwhile, wrap the tortillas in aluminum foil and heat in oven until warm and slightly softened, about 5 minutes.
In a large bowl, combine the cod, ginger, and remaining lime juice. Divide the fish, arugula, and guacamole among the tortillas.