A traditional Niçoise salad brings together bright Mediterranean flavors in a single satisfying bowl. Crisp mixed greens provide a fresh base for rich oil-packed tuna, briny olives, and tender hard-boiled eggs. Sweet cherry tomatoes add a burst of color and acidity to balance the savory elements. Everything gets tied together with a sharp, punchy shallot vinaigrette made from red wine vinegar, lemon juice, and grainy mustard. It makes an excellent light lunch or a refreshing dinner on a warm evening.