Preheat the oven to 425F and place a baking sheet in the oven to heat along with the oven..
Trim and divide the tilapia fillets in half lengthwise if purchased as whole fish fillet. Place the fillets on a plate or cutting board and sprinkle both sides and the edges generously with the cajun seasoning, then set aside.
Prepare the avocado sauce by adding the tartar sauce, avocado, cilantro, juice of 1 lime and a pinch of kosher salt to a food processor or a small bowl and process or mash until smooth. Add more lime juice and kosher salt to taste. Set aside.
In a medium size bowl, toss the cabbage with the juice of 1 lime and a sprinkling of kosher salt and set aside.
Once the oven has come to temperature, spray the hot sheet pan with cooking spray and place the seasoned fish on the baking sheet and lightly mist with oil or cooking spray. Cook the fish until they are opaque and easily flake with a fork, about 12-15 minutes.
Meanwhile, spray a large non-stick skillet with cooking spray and heat over medium high heat. Add the tortillas one at a time to the pan and spray the tortillas lightly with the cooking spray. Cook for 1-2 minutes or until lightly golden on each side. Transfer to a plate lined with a paper towel. Continue with all of the tortillas.
To assemble the tacos, layer two tortillas together and place some slaw in the bottom of the tortilla with a few chunks of the fish. Add a spoonful of the avocado sauce and sprinkle with additional cilantro and a squeeze of lime, and serve.