Make the marinade: Whisk together olive oil, lemon juice, red wine vinegar, garlic, oregano, cumin, salt, and pepper in a small bowl until combined.
Prep the cauliflower: Cut into small, even florets. For a softer texture, blanch in boiling salted water for 2 minutes then transfer to ice water immediately. Pat dry thoroughly.
Marinate: Toss cauliflower with the marinade in a large bowl, making sure every floret is coated evenly.
Add vegetables: Stir in the olives, cherry tomatoes, and red onion. Mix gently to combine.
Chill: Cover and refrigerate for at least 1 hour, up to 4 hours for best flavor.
Finish and serve: Fold in crumbled feta and fresh herbs just before serving. Taste and adjust salt or lemon juice as needed.