01 - Whisk together olive oil, lime juice, ground cumin, smoked paprika, garlic powder, sea salt, and black pepper in a shallow bowl until thoroughly combined.
02 - Place fish fillets into the marinade, turning to coat completely. Let sit at room temperature for 15 minutes to absorb flavors.
03 - Heat grill to medium-high temperature (approximately 400°F). Lightly oil the grates to prevent sticking.
04 - Place marinated fish on the grill and cook for 3 to 4 minutes per side until flesh is opaque and flakes easily with a fork. Transfer to a plate and let rest for 5 minutes.
05 - Combine sour cream, lime juice, chopped cilantro, salt, and pepper in a small bowl. Mix until smooth and refrigerate until ready to serve.
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 - Flake the rested grilled fish into large chunks using a fork, discarding any skin or bones.
08 - Layer shredded cabbage, flaked fish, diced tomatoes, sliced avocado, crumbled cheese, and fresh cilantro onto each warmed tortilla. Drizzle generously with prepared sauce.
09 - Arrange tacos on a serving platter with fresh lime wedges on the side. Serve immediately while tortillas are warm and fish is still tender.