Place potato in a medium saucepan; cover with water. Bring to a boil; reduce heat, and simmer 10 minutes. Add beans, adding more water to cover, if necessary. Simmer 5 minutes or until vegetables are tender. Drain and rinse under cold water; let cool slightly. Set aside.
Drain tuna, reserving liquid. Flake tuna into bite-size pieces. Combine reserved liquid, olives, vinaigrette, salt, and pepper in a bowl. Add tuna, potato, and beans; toss gently. Chill.