1. In a saucepan, bring the water to a boil. Add the quinoa, reduce heat to low, cover, and simmer for about 15 minutes or until the water is absorbed and the quinoa is tender. Let it cool.
2. In a mixing bowl, combine the cooked quinoa, red onion, parsley, lemon juice, olive oil, salt, and black pepper. Mix well.
3. Arrange the cucumber slices on a serving platter. Top each slice with a spoonful of the quinoa mixture.
4. Serve immediately or refrigerate until ready to serve.