Rinse the quinoa under cool water, then combine with 2 cups of water in a medium saucepan. Bring to a rapid simmer, then turn down the heat to medium-low, cover, and cook until the quinoa is fluffy and chewy, about 20 minutes.
Stir the onions, tomatoes, parsley, mint, and garlic into the warm quinoa.
Whisk together the olive oil and lemon juice and add salt and pepper to taste.
Pour this over the salad and stir to combine.
Notes
Serve room temperature or cold. This salad is even better the next day, once the flavors have had a chance to mingle.