Thinly shred the cabbage and place in a medium bowl with 1 teaspoon of the salt and the lime juice. Massage the salt into the cabbage. Mix the sour cream and sriracha in a small bowl. Pit and slice the avocado and set everything aside.
Heat the oven to 200°F. Line a rimmed baking sheet with paper towels and place the thawed cod on the sheet. Cover with another paper towel and set aside.
Combine the salt, spices, and sugar together in a small bowl. Dip the cod filets into the bowl to coat the filets on both sides. Heat a nonstick or well-seasoned cast iron skillet to medium-high and when it’s hot, add the cooking oil. Turn on your vent fan. When the oil is hot, place the cod in the pan and sear for 3 to 4 minutes on each side (more if the filets are thicker than ½-inch). You may need to do this in batches. Transfer the cooked cod on a baking sheet and place in oven to keep warm.
Leave the cod in the oven while you heat up the tortillas. Cover the warm tortillas with a towel and transfer cod to a platter with the cilantro, jalapenos, and lime wedges. Bring to the table along with the sour cream and cabbage and serve family-style.