Thickly slice the avocados lengthwise and coat with the lime juice to prevent browning; set aside. In a small saucepan, over medium-high heat, bring the vinegar, tamari and honey to a low boil. Lower the heat and simmer until syrupy, 6 to 7 minutes. Set aside.
In a large skillet, heat the oil over high heat. Sprinkle the tuna with the five-spice powder and season with salt and pepper. Place the tuna in the skillet and cook, turning once, until just browned, 1 to 2 minutes on each side. Slice the tuna and top with the sesame seeds and chives.
Divide the lettuce among 4 plates and top with the tuna and avocado. Drizzle with the dressing.