Rinse quinoa in a fine sieve until water runs clear, drain and transfer to a medium pot. Add water and salt and bring to a boil. Cover, reduce heat to medium low and simmer until water is absorbed, 15 to 20 minutes. Set aside off the heat for 5 minutes; uncover and fluff with a fork.
Mix quinoa, beans, corn, red onion, tomatoes, and cilantro together in a serving plate.
Whisk olive oil, lime juice, garlic, salt, and black pepper in a bowl; pour over quinoa mixture and toss to coat. Cover bowl with plastic wrap and refrigerate until flavors blend, at least 2 hours. Stir again before serving.