Oil your grill with olive oil, then heat to medium. Grill fish over medium heat, 2 to 3 mins. each side. While fish is grilling, warm a few tortillas at a time by spraying lightly with water and placing on the grill. Turn frequently, and remove to a kitchen towel to keep warm. In a small bowl, combine mayonnaise, ketchup, and crema. When fish is done, place 2 strips on each tortilla, top with shredded cabbage, chopped tomatoes and a spoonful of sauce. Serve with lime wedges and salsa.