Bring water and and quinoa to a boil in a saucepan. Reduce heat to medium-low, cover, and simmer until quinoa is tender and water has been absorbed, 15 to 20 minutes. Set aside to cool.
Whisk olive oil, lime juice, cumin, and 1 teaspoon salt together in a bowl to make dressing.
Combine cooled quinoa, black beans, and cucumber in a large bowl. Pour in dressing and toss to coat. Stir in cilantro and season with salt and pepper. Refrigerate or serve immediately.
