Toss the cabbage, onion and jalapeno with the vinegar and 2 teaspoons of the oil, and season generously with salt and pepper. Set aside.
Heat a large dry skillet over medium high heat. Heat the torillas one at a time, cooking for about 30 to 60 seconds on each side, until it is browned in spots and smells slightly toasty. Stack the tortillas on a plate as they are cooked, and repeat until all of the tortillsas have been toasted. Set aside.
Sprinkle the pieces of fish all over with the cumin, chili powder, and salt and pepper. Heat 2 tablespoons of the oil in the large skillet over medium high heat. Add 1/3 of the fish and sauté until almost cooked through, turning it as needed, about 5 minutes in all. The pieces may fall apart a little as you cook them; that’s perfectly fine. During the last minute of cooking each batch, add about 1/3 of the garlic and toss over the heat. Place the fish on a serving plate as it is cooked and sprinkle each batch with 1 teaspoon of the lime juice. Keep going, adding a bit more oil as needed, and then adding the fish to the same plate as it is cooked, until all of the fish is sautéed and sprinkled with juice.
Serve the fish with the toasted tortillas, cabbage slaw, and the toppings you like. Let everyone assemble their own tacos.