Rinse the quinoa for about 2 minutes, using your hands to remove any saponins.

Cook the quinoa: fill a medium pot with water, add quinoa and salt to taste, bring to a boil. Reduce heat to low, cover, and simmer for 15 minutes.

Remove from heat and keep covered for 5 minutes. Fluff with a fork and transfer to a large bowl to cool.

Dice all vegetables while quinoa cools.

Add diced red onion, olives, cucumber, and cherry tomatoes to the cooled quinoa. Squeeze half a lemon over the mixture.

Drizzle olive oil over the mixture. Add feta cheese, salt, and pepper. Toss well to combine.

Taste and adjust seasoning or lemon juice as needed before serving.