To make white sauce:
In a medium bowl, mix together yogurt, and mayo.
Gradually stir in lime juice until the consistency is slightly runny. Season with pepper flakes, capers, oregano, cumin, dill, and cayenne.
Set aside. (If you're able, give the sauce a couple of hours to sit before serving - to let the flavors meld)
Marinate the fish in a mixture of olive oil, lime juice, salt, and pepper for at least an hour before grilling or pan-frying the fish
(The Mahi-Mahi marinated in lime juice and olive oil is absolutely delicious. It's my favorite part!)
To serve, place grilled fish in a tortilla, and top with white sauce, shredded cabbage, onion, avocado, and tomatoes