1. Cover potatoes with 2 inches water in a small saucepan; bring to a boil. Simmer 15 minutes or until fork-tender; drain and transfer to a bowl, reserving cooking water. Halve potatoes, and toss in 1 tablespoon vinegar. Arrange on a platter.
2. Add the green beans to simmering water; cook 4 minutes or until crisp-tender. Drain; rinse with cold water until cool. Transfer to platter.
3. Preheat grill, and lightly oil rack.
4. Whisk together remaining 1 tablespoon vinegar with mustard in a small bowl, and add olive oil in a slow stream until well-combined. Transfer 2 teaspoons vinaigrette to a bowl, and toss with tuna to coat. Whisk remaining vinaigrette with 1 tablespoon hot water and olives.
5. Drain skewers; thread 2 with tuna and remainder with vegetables. Grill fish and vegetables, turning occasionally, over moderate heat 6–8 minutes or until fish is cooked through and vegetables are tender. Remove from skewers; place on platter with eggs. Drizzle with vinaigrette.
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