01 - Whisk together olive oil, lime juice, cumin, smoked paprika, garlic powder, sea salt, and black pepper in a shallow bowl until fully combined.
02 - Add fish fillets to the marinade, turning to coat evenly. 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. Cook for 3 to 4 minutes per side until the fish is opaque throughout and flakes easily with a fork. Transfer to a plate and let rest for 5 minutes.
05 - While fish grills, 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 directly on the grill for 30 seconds per side until pliable and slightly charred. Wrap in a clean towel to keep warm.
07 - Using a fork, flake the rested grilled fish into large chunks, discarding any skin or bones.
08 - Layer each warm tortilla with shredded cabbage, flaked fish, diced tomatoes, avocado slices, crumbled cheese, and fresh cilantro. Drizzle generously with the cream sauce.
09 - Arrange tacos on a serving platter with fresh lime wedges on the side. Serve immediately while fish is still warm.