Prepare quinoa as directed on package. Allow to cool for five minutes after completion of cooking.
Add oil and vinegar to quinoa and allow mixture to come to room temperature. Meanwhile, dice onion, pepper and tomato; chop olives and cilantro.
Add quinoa, veggies, cilantro, salt, pepper and crumbled cheese to a large bowl, squeeze with fresh lemon juice from half the lemon, reserving the other half for garnish. Toss to combine.