01 - In a shallow bowl, whisk together olive oil, lime juice, ground cumin, smoked paprika, garlic powder, sea salt, and black pepper until thoroughly combined.
02 - Add fish fillets to the bowl, turning to coat evenly on all sides. Let marinate at room temperature for 15 minutes, allowing flavors to penetrate the fish.
03 - Heat grill to medium-high temperature (approximately 375°F). Lightly oil the grates to prevent sticking.
04 - Place marinated fish on the grill. Cook for 3 to 4 minutes per side until fish is opaque throughout and flakes easily with a fork. Remove from heat and let rest for 5 minutes.
05 - While fish cooks, combine sour cream (or Greek yogurt), lime juice, chopped cilantro, salt, and pepper in a small bowl. Mix until smooth and refrigerate until serving.
06 - Place corn tortillas on the grill for 30 seconds per side until pliable and lightly charred. Keep warm wrapped in a clean kitchen towel.
07 - Using a fork, break the rested grilled fish into large, chunky pieces, removing any bones if present.
08 - Layer each warm tortilla with shredded cabbage, flaked fish, diced tomatoes, sliced avocado, crumbled cheese, and fresh cilantro. Drizzle generously with the prepared sauce.
09 - Arrange tacos on a serving platter and accompany with fresh lime wedges. Serve while tortillas are warm and fish is still tender.