Rinse quinoa thoroughly and cook in boiling water, then let it cool.
Finely chop cucumber, tomato, and onion.
Cut feta cheese into bite-sized pieces.
In a bowl, combine quinoa, chopped veggies, and feta cheese.
Make a dressing with olive oil, lemon juice, salt, and pepper, then mix well.
Lightly toss the ingredients with the dressing.
Arrange on a plate to serve.