How to Make It
Fill a medium-sized saucepan with 1 cup water. Add the rinsed quinoa and stir to combine. Bring to a boil, cover, and reduce heat to low. Cook, covered, until the water is absorbed and the quinoa is tender, about 15-18 minutes. Remove from heat and fluff the quinoa with a fork. Let cool.
In a large bowl, whisk together the lemon juice, oil, salt, and several grinds of pepper. Add the cooled quinoa, cucumber, tomatoes, parsley, onion, and mint and toss to combine, adding more lemon juice to taste. Serve cold or at room temperature. Tabbouleh can be made up to 4 days ahead. Refrigerate in an airtight container.