Marinate the white fish fillet in lime juice, salt, garlic powder and black pepper for at least 15 minutes.
While waiting, heat corn tortillas as per package instructions or on a dry pan over medium-high flame until slightly charred
Warm up the mayonnaise in microwave oven (about 30 seconds) to make it easier for spreading
Assemble tacos by placing marinated fish fillet on top of warmed tortilla, add a spoonful of warm mayo and optional garnishes such as shredded cabbage or avocado.