Combine the ingredients for the Blackened seasoning in a small bowl and stir to combine. Set aside.
To prepare the coleslaw, add the sliced cabbage, kale leaves (if using), and shredded carrot to a large, non-reactive bowl. Whisk the Greek yogurt, apple cider vinegar, ground cumin, Dijon mustard, and lime juice together in a smaller bowl and pour over top of the other vegetables. Season with salt and black pepper, to taste, and toss to combine. Set aside.
Generously season both sides of the mahi-mahi with the blackened seasoning and rub to cover the entire fish and to make sure it adheres well. Carefully slice the fish into bite-sized pieces and set aside.
Note: You can slice the fish before seasoning, but it takes longer to coat each piece individually and the blackened flavor will be much stronger if all sides are coated.
Add the olive oil to a large cast iron or other skillet over medium heat. Once heated, add the seasoned fish and cook until opaque and flakey, approximately 3-4 minutes per side. Remove from heat and set aside.
To serve, evenly divide the creamy coleslaw and blackened fish between the 8 tortillas. Top with the sliced radishes and fresh cilantro leaves. If desired, drizzle some Creamy Avocado Sauce on top. Enjoy!