In a large bowl combine the olive oil, vinegar, basil, parsley, salt, and pepper.
Add the onion, tomatoes, watercress, olives and toss to combine. Add the feta and gently toss to combine again. Serve at room temperature.
Notes
Do you love watercress? I LOVE watercress, which I know is a slightly weird thing to say (or even to know about oneself). But it seems like it’s not all that available, and when you can find it, it’s pricey or just not looking all that fresh and perky. It’s a fragile green with a short shelf life, but it’s so amazingly fresh and kind of grassy tasting in a great way that we all need to persevere and find it and use it.