For the quinoa. Place the washed quinoa to two cups of water in a large saucepan. Add olive oil and bring to boil on medium high heat then reduce the heat to low. The cooking should take 10- 15 minutes. Cook until ready and set aside to cool.
In a large bowl, add the cooked black beans, corn, the chopped red onion, tomatoes, and cilantro. Mix until well and add the cooled cooked quinoa and the diced avocados. Toss to combine well. Do not overmix, doing so will break the avocados and make them watery.
Add lemon juice and salt then combine. Chill for about 10 minutes to set.
Serve as desired.
You can keep the remaining salad in the refrigerator. The mixture can stay fresh for at least three days if refrigerated.