Blanch the green beans in boiling water for 3 minutes, then transfer to a bowl of ice water to stop the cooking process.
In a small bowl, whisk together olive oil, red wine vinegar, Dijon mustard, salt, and pepper to make the dressing.
Arrange green beans, potatoes, hard-boiled eggs, tuna, tomato slices, and black olives on a plate.
Drizzle the dressing over the salad and toss gently to combine.
Serve immediately, garnished with additional salt and pepper if desired.