Prepare a smoker for hot smoking by soaking and then igniting 3 large hardwood chunks, and regulating the temperature so that it will remain between 170 degrees and 250 degrees. Smoke the fish for 1 to 1 1/4 hours, or until the flesh is flaky and cooked through. Shred the flesh and refrigerate until ready to serve.
In a blender, combine the vinegar, garlic, salt, pepper, sugar, avocado, and olive oil and blend for 1 minute, until completely smooth and emulsified. Transfer to a glass bowl, stir in the green onions, and taste for seasoning. Cover with plastic wrap and refrigerate for 2 hours.
When ready to serve, drain the onion slices, pat them dry, and separate them into rings. In a large mixing bowl, toss the spinach, lettuce, and tomatoes, together gently. Pour on enough dressing to coat, and toss again just to mix. Place a mound of the salad on each of 6 plates and scatter about 2 ounces of the shredded swordfish over the salad. Drape a few onion rings over the top and serve.
There are many excellent kettlestyle home smokers on the market, all of which must be used outdoors. It is also possible to use a wok lined with aluminum foil to smoke foods in a well ventilated kitchen. Soak the hardwood chunks for at least 3 hours and place them in the bottom of the foil lined wok. Place a round metal rack above the chunks. Heat the wok over medium heat, partially covered, until the wood starts to smoke. Place the food to be smoked on the rack and again partially cover the wok. Keep the heat just high enough to maintain the smoldering of the chips. Use a thermometer with a cable and a probe to monitor the temperature at the rack level and adjust the heat as necessary.