To roast jalapeños for the slaw and topping, heat a tablespoon of canola oil over medium-high heat, then add peppers and cook until softened and blistered on all sides. Peel the skin by scraping it off with a knife. Season with salt, then set aside.
To make the slaw, combine all ingredients in a large bowl and mix thoroughly, then refrigerate until ready to serve. Combine all sauce ingredients in a small bowl, whisking thoroughly, and refrigerate. For the fish, combine the spices and add salt to taste. Cut fish into 1-inch strips, coat with spice mix, and set aside. Heat oil in a large nonstick pan over medium-high heat. Sear fish, flipping halfway through, until it is cooked through and flakes easily with a fork, approximately 5 minutes. Assemble tacos with fish, slaw, sauce, and desired toppings, then serve!