Blanch the green beans by boiling them for 2-3 minutes, then immediately transferring them to an ice water bath to stop the cooking. Drain and set aside.
1 cup green bean
In a small bowl, whisk together the olive oil, red wine vinegar, Dijon mustard, garlic, salt and pepper until well combined.
3 tbsp olive oil, 2 tbsp red wine vinegar, 1 tbsp Dijon mustard, 1 clove garlic, ⅛ tsp salt, 1 pinch pepper
On a large serving platter or individual plates, arrange the mixed greens as a base. Add the cherry tomatoes, red onion, green beans, hard boiled eggs, potatoes, tuna, and capers (if using).
4 cups mixed greens, 1 cup tomato, ¼ cup red onion, 4 egg, 1 cup potato, 5 oz tuna, ¼ cup capers
Drizzle the dressing evenly over the salad just before serving.