Warm the sunflower oil in a large nonstick skillet over medium heat. Add the garlic and sauté for 1 minute. Season the cod filets with pepper on each side, and cook until firm and very lightly browned, about 4 minutes per side. Transfer cooked fish to a plate and allow to rest for 1 minute, and then slice.
Serve the fish in the soft taco tortillas with lettuce leaves, bell pepper, cilantro, green onions, and a squeeze of lime juice.