1. Cook quinoa: In a pot, bring quinoa and water to a boil. Reduce heat to low, cover, and simmer for 15 minutes. Remove from heat and let it sit for 5 minutes, then fluff with a fork.
2. Prepare vegetables: While quinoa is cooking, chop the cherry tomatoes, cucumber, red onion, and olives.
3. Mix salad: In a large mixing bowl, combine cooked quinoa, chopped vegetables, and crumbled feta cheese.
4. Make dressing: In a small bowl, whisk together olive oil, lemon juice, dried oregano, salt, and pepper.
5. Combine: Pour the dressing over the salad and toss to combine. Adjust seasoning with salt and pepper if needed.
6. Serve: Serve immediately or chill in the fridge for 30 minutes for the flavors to meld.