Make Avocado Crema: In a small blender or food processor, combine the flesh of the avocado, Greek yogurt, lime juice, and a pinch of salt. Blend until completely smooth. Set aside.
Make Seasoning: In a small bowl, whisk together all the ingredients for the blackened seasoning: smoked paprika, garlic powder, onion powder, oregano, cumin, cayenne, salt, and pepper.
Season Fish: Pat the fish fillets completely dry with a paper towel. Rub the spice blend generously on all sides of the fish.
Cook Fish: Heat the olive oil in a large non-stick skillet over medium-high heat. Carefully place the seasoned fillets in the hot pan. Cook for 3-4 minutes per side, until the seasoning is dark and fragrant and the fish flakes easily with a fork.
Assemble: Remove the fish from the skillet and gently break it into large chunks. To assemble the tacos, fill each warm tortilla with a portion of the blackened fish, a handful of shredded cabbage, a generous drizzle of the avocado crema, and a sprinkle of fresh cilantro. Serve immediately with extra lime wedges.