Rinse the quinoa thoroughly under cold water in a fine-mesh sieve to remove the bitter saponin coating.
In a medium saucepan, combine the rinsed quinoa with 2 cups of water and a pinch of salt. Bring to a boil.
Once boiling, reduce heat to low, cover, and simmer for 15 minutes until the quinoa is fluffy and water is absorbed.
Remove from heat and let the quinoa sit, covered, for 5 minutes. Fluff with a fork and spread on a baking sheet to cool for 10-15 minutes.
While the quinoa cools, drain and rinse the black beans thoroughly under cold water.
In a large bowl, combine the cooled quinoa, black beans, corn, diced red bell pepper, and chopped cilantro.
In a small bowl, whisk together the lime juice, olive oil, salt, and pepper. Add optional cumin and chili powder if desired.
Pour the dressing over the salad ingredients and toss gently until everything is evenly coated. Taste and adjust seasoning.
Chill the salad in the refrigerator for at least 20 minutes before serving to allow flavors to develop.
If using optional avocado, fold it in just before serving to prevent browning.
