Red cabbage carrot slaw: Cut the red cabbage into very thin strips (the more thinly the better), grate the carrot on the small holes of a box grater. Add the olive oil and lime juice, season with salt and pepper to taste, toss until combined. Set aside. It's good to make this slaw ahead and let it sit for 1-2 hours to let the cabbage soften.
Prepare the fish: pat dry the fish fillets with paper towels, then rub with cajun seasoning. My cajun seasoning already contains salt, so I haven't added any. Sprinkle the fish with flour, then rub the flour on all sides of the fillets. Set aside.
Make the mango salsa: Cut the mango into small cubes, toss with chopped cilantro, olive oil, lime juice, and chili flakes (if using). Season with salt and pepper to taste and optionally with more lime juice if your mango is very sweet.
Make the mango sauce: blend all the sauce ingredients in a food processor, season to taste with salt and pepper.
Pan-fry the fish fillets: Heat the clarified butter (or frying oil) over high heat in a frying pan. Coat the fish fillets once again in flour (after rubbing the fish with spices it will release some water and absorb the first portion of flour so now we can add more flour. Thank's to that, the flour coating with be thicker and more crispy). Once the pan is hot add the fish fillets. Cook on one side until browned then flip over and cook until cooked through.
How to check if the fish is cooked through: the color will turn from opaque to white and the fish can be easily flaked with a fork. To be sure it's best to measure the internal temperature of the fish with a thermometer. Stick the thermometer into the thickest part of the fish, the temperature should be 145°F/ 63°C.
Assemble: Place some slaw over the tortillas, top with mango salsa and fish cut into smaller pieces. Pour over the sauce. You can sprinkle the tacos with additional lime juice and cilantro.