In a medium saucepan over medium-high heat, bring water to a boil. Add the potatoes and cook until fork tender, about 10-15 minutes. Remove the potatoes with a slotted spoon leaving the water in the pot. Cut the potatoes in halves or quarters, and set aside.

In the same saucepan, bring water to a boil again. Add the green beans and cook for 3-4 minutes or until crisp-tender. Drain and transfer the green beans to a bowl of ice water to cool (ice bath). Once cooled, drain and set aside.

Place the eggs in a saucepan and cover with water. Bring to a boil, then reduce the heat and simmer for 6-10 minutes- depending on how you like the yolk done. Drain the eggs and transfer them to a bowl of ice water. Let them cool for a few minutes, then peel and cut them into quarters.

Whisk together the olive oil, red wine vinegar, Dijon mustard, minced garlic, salt, and pepper in a small bowl until well combined. Set aside. You can also combine all the dressing ingredients in a small jar with a lid and shake. 

In a large platter or salad bowl, arrange the salad greens. Arrange the cooked potatoes, green beans, cherry tomatoes, Kalamata olives, capers, sliced red onion, tuna, and hard-boiled eggs over the top of the greens. 

Drizzle the vinaigrette dressing over the composed salad and let it sit for a few minutes. When ready to serve, gently toss to combine to avoid breaking up the eggs—season with additional salt and pepper to taste.

Divide the salad onto individual plates and serve.