Pat the cod fillets dry with a paper towel and season both sides evenly with chili powder, cumin, garlic powder, sea salt, and black pepper.
In a medium bowl, combine the shredded cabbage, lime juice, and chopped cilantro to create a bright, zesty slaw.
Heat the olive oil in a large non-stick skillet over medium-high heat until shimmering.
Place the cod in the skillet and sear for 3 to 4 minutes per side until the exterior is golden and the fish flakes easily with a fork.
Briefly warm the corn tortillas in a separate dry pan or directly over a low gas flame until they are soft and pliable.
Flake the cooked cod into large, tender pieces and distribute them evenly among the warm tortillas.
Top each taco with the cabbage slaw, sliced avocado, and a dollop of Greek yogurt before serving.