01 - Whisk together olive oil, lime juice, cumin, paprika, garlic powder, salt, and pepper in a shallow bowl until thoroughly combined.
02 - Add fish fillets to the marinade, turning to coat completely. Let rest for 15 minutes at room temperature 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 3-4 minutes per side until the flesh is opaque 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 on the grill for 30 seconds per side until pliable and lightly charred. Keep warm wrapped in a clean kitchen towel.
07 - Break the rested grilled fish into large chunks using a fork, discarding any skin.
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 with lime wedges on the side. Serve immediately while tortillas are warm and fish is tender.