First, using a strainer, rinse the black quinoa under cold water. Add quinoa, water, and salt to a medium saucepan and bring to a boil over medium heat. Boil for 5 minutes. Turn the heat to low and simmer for about 15 minutes, or until water is absorbed. Remove from heat and fluff with a fork. Let cool quinoa cool to room temperature.

In a large bowl, combine quinoa, mango, tomatoes, green onions, cilantro, and avocados. In a small bowl, whisk together lime juice, olive oil, and cumin. Pour the dressing over the quinoa salad and gently stir until well combined. Season with salt and pepper. Serve at room temperature or chilled.