For the salmon: Preheat the oven to 350 degrees F. In a small bowl, combine the chili powder, salt, brown sugar, cumin, pepper, coriander and cayenne.
Sprinkle the salmon fillet with a generously with the spice mix and rest the fish for 1 hour.
Roast the salmon in the oven until fully cooked, 15 to 20 minutes. Remove the salmon from the oven and cool slightly. Flake the salmon into medium chunks and season with salt and pepper.
For the slaw: In a bowl, combine the vinegar, oil, soy sauce, sugar and lime juice, and whisk until the sugar dissolves.
Add the cabbage, carrots and scallions, and mix well to coat all of the slaw with the dressing. Refrigerate the slaw for at least 1 hour before using.
For plating: Heat a cast-iron griddle over high heat until the griddle begins to smoke. Warm the tortillas on the griddle without any oil, just until they are pliable.
Heat the oil on the griddle and add the flaked salmon to bring back up to temperature if the salmon has cooled. (If the salmon is hot out of the oven skip this step.)
Place about 3 ounces of flaked salmon in the center of each tortilla and top with 2 ounces of slaw. Plate 2 tacos with a lime wedge for each serving.