Prepare the Beans: Rinse and drain the beans thoroughly to remove excess sodium and ensure freshness.
Combine Vegetables: In a large mixing bowl, toss together the tomatoes, onion, parsley, and cucumber.
Make the Dressing: Whisk olive oil, lemon juice, vinegar, Dijon mustard, garlic, salt, and pepper in a small bowl until emulsified.
Mix Everything Together: Add the beans to the vegetable mixture, pour over the dressing, and toss well to combine.
Optional Additions: Sprinkle with feta cheese for extra creaminess.
Serve: Serve immediately or chill for 30 minutes to enhance flavors.