In a small saucepan, bring water to a boil. Add quinoa and give it a quick stir. Cover the saucepan, reduce heat to low and simmer for 15 minutes, or until the quinoa is tender and the water has been absorbed. Remove from heat and let stand 5 minutes. Then fluff with a fork. Allow it to cool to room temperature.
In a large bowl, combine quinoa, tomatoes, mint, and avocado. In a small bowl, whisk together the olive oil, soy sauce, lemon juice, pepper and salt. Pour the dressing over the quinoa mixture and toss. Taste and adjust seasonings. Serve avocado quinoa salad at room temperature.