Cover the quinoa with cold water and let it sit for 5-10 minutes. Put it in a fine mesh colander and rinse until the water runs clear. Transfer to a medium saucepan. Cover with 3 cups water and salt and bring to a boil. Reduce heat to low, and simmer 15 minutes. Drain excess water, cover the pot with a dish towel, replace the lid, and let it sit for 10 minutes.
Combine the cucumber, tomato, cilantro, onion, olive oil, lime juice, and vinegar.
Stir the quinoa into the veggies. Serve with chopped avocado on top.