Tuna Nicoise Sandwich

INGREDIENTS

• 3 tablespoons extra-virgin olive oil
• 2 tablespoons white-wine vinegar
• 1 tablespoon Dijon mustard
• Coarse salt and ground pepper
• 2 cans oil-packed tuna (6 ounces each), drained
• 1/4 English cucumber
• 1/2 small red onion
• 1 8-inch round loaf country-style bread
• 3 tablespoons jarred olive tapenade
• 1 cup fresh basil leaves
• 2 large eggs, hard-cooked and sliced