Blanch the cauliflower in a large pot of salted boiling water for 2 to 3 minutes until just slightly tender.
Ice bath: Transfer immediately to a bowl of ice water for 5 minutes, then drain and pat dry thoroughly.
Make the dressing by whisking together olive oil, red wine vinegar, lemon juice, oregano, garlic powder, salt, and pepper.
Combine cauliflower, cherry tomatoes, red onion, and olives in a large bowl. Pour dressing over everything and toss gently.
Marinate covered in the refrigerator for at least 30 minutes before serving.
Finish by folding in crumbled feta and fresh parsley just before serving.