01 - Combine olive oil, lime juice, ground cumin, smoked paprika, garlic powder, sea salt, and black pepper in a shallow bowl. Whisk until thoroughly blended.
02 - Place white fish fillets into the marinade, turning to coat completely. Let sit 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 preheated grill. Cook for 3 to 4 minutes per side until the flesh is opaque and flakes easily with a fork. Remove from heat and let rest for 5 minutes.
05 - While fish grills, mix sour cream (or Greek yogurt), lime juice, chopped cilantro, salt, and pepper in a small bowl until smooth. 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 - Using a fork, break the rested grilled fish into large, bite-sized chunks, discarding any skin if present.
08 - Layer each warmed tortilla with shredded red 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 fresh lime wedges on the side. Serve immediately while tortillas are warm and fish is at peak flavor.