Start by boiling the potatoes until tender but not mushy. At the same time, cook green beans until bright green and crisp. Hard-boil the eggs, then cool them in cold water for easy peeling.
In a small bowl, whisk olive oil, lemon juice, Dijon mustard, salt, and pepper. The mixture should look slightly thick and well blended. This dressing ties all the ingredients together beautifully.
Layer potatoes, green beans, tomatoes, onions, and olives in a bowl. Add flaked tuna and sliced eggs on top for protein richness. Drizzle dressing evenly so every bite is flavorful and fresh