Bring quinoa and water to boil in saucepan. Reduce heat to medium-low, cover, and simmer until quinoa is tender and water has been absorbed, 10-15 minutes. Set aside to cool.

Whisk olive oil, lime juice, cumin, 1 teaspoon salt, and red pepper flakes together in a bowl.

Combine quinoa, tomatoes, black beans, and green onions in a bowl. Pour dressing over quinoa mixture; toss to coat. Stir in cilantro n season with salt and black pepper. Serve immediately or chill in refrigerator.