At least an hour before you plan to serve the tacos, toss the cabbage, cucumber, vinegar, dill, 1 teaspoon salt, and 1/2 teaspoon black pepper together in a large bowl. Cover and refrigerate, allowing the cabbage to marinate.
Brush a baking dish with olive oil and place the salmon in it. Mix the chili powder, lime zest, and 1 1/2 teaspoons salt in a small bowl. Brush the salmon with 1 tablespoon of the lime juice and sprinkle with the chipotle seasoning mixture. Roast for 12 to 15 minutes, depending on the thickness of the fish, until the salmon is just cooked through.
Wrap the tortillas in 2 foil packets and place them in the oven with the salmon. Roughly mash the avocados with the remaining 2 tablespoons of lime juice, the Sriracha, 1 teaspoon salt, and 1/4 teaspoon black pepper.
To serve, lay 2 warm tortillas on each of 6 plates. Place a dollop of the avocado mixture on one side of each tortilla, then some large chunks of salmon, and finally, some of the slaw. Fold the tortillas in half over the filling (they will be messy!) and serve warm.