In a small food processor, pulse together avocado, fresh basil, chopped fresh chives, olive oil, lemon juice, fresh garlic, ⅛ teaspoon salt, and pepper until mostly broken down. Then process until well combined and creamy. Scrape into a medium bowl.
Drain tuna filets, cut into large chunks, and add to green goddess dressing along with celery, scallions and remaining ⅛ teaspoon salt. Gently fold together until tuna is evenly coated.
Warm or toast sandwich thins.
To assemble each sandwich, scoop half the tuna mix on a sandwich thin, cover with half of the shredded cabbage (about 9 grams) and top with another sandwich thin.