Grilled sesame tuna with new-potato salad

1/2 cup rice vinegar, divided
1 tablespoon sesame oil
2 tablespoons hoisin sauce
4 4-ounce tuna steaks (about 1-inch thick)
6 small red potatoes, quartered
1 cup string beans, ends trimmed
1/4 cup minced red onion
1/4 cup chopped fresh parsley
salt and black pepper to taste

1. Preheat grill, grill pan or broiler.
2. In a shallow dish, add 1/4 cup of rice vinegar to sesame oil and hoisin sauce. Add tuna steaks and turn to coat. Grill or broil 5-7 minutes per side.
3. Meanwhile, cook potatoes for 7 minutes in a large pot of rapidly boiling water. Add string beans and cook 1-2 more minutes, until potatoes are fork-tender and string beans are crisp-tender. While still warm, toss with remaining 1/4 cup vinegar, red onion and parsley. Add salt and pepper.
4. To serve, place 1 tuna steak on each plate next to 3/4 cup of warm new-potato salad.