In a medium saucepan over high heat, bring the water to a boil. Add the quinoa and stir.
Once the water has reduced, lower the heat to medium-low and simmer covered until quinoa is tender but still chewy (about 15 to 20 minutes) Turn it off and let cool completely.
In another bowl, combine the tomato, onion, cilantro, jalapeño pepper, lemon juice, salt, and olive oil. Add the quinoa and mix well. Taste for salt and let it chill in the fridge for at least 20 minutes.