Prepare all vegetables: dice cucumbers and tomatoes, thinly slice red onion, and halve olives if desired.
In a small bowl, whisk together olive oil, lemon juice, minced garlic, oregano, salt, and pepper until well combined.
Place diced cucumbers, tomatoes, sliced red onion, and olives in a large serving bowl.
Pour about three-quarters of the dressing over the vegetables and toss gently to coat everything evenly.
Add the crumbled or cubed feta cheese to the bowl.
Drizzle the remaining dressing over the feta and vegetables, then fold everything together carefully to distribute the feta without breaking it up too much.
Let the salad sit at room temperature for 10-15 minutes to allow flavors to meld.
Garnish with fresh dill or parsley if using, then serve immediately.