1. Heat an indoor grill, or prepare an outdoor grill with hot coals, or heat a gas grill to hot, or heat an oven broiler.
2. In a medium-size saucepan of salted boiling water, cook the green beans until crisp-tender, 6 to 7 minutes. Drain the beans; let cool.Dressing:
3. In small bowl, whisk together the vinegar, mustard, garlic salt and pepper. Gradually whisk in olive oil until dressing is thick and smooth and well blended.Tuna Salad:
4. Season tuna with salt and pepper. Grill or broil 3 minutes. Turn tuna steaks over; grill until cooked through, about 2 minutes. Brush tuna with 2 tablespoons dressing. Set aside.
5. In large bowl, combine green beans, salad blend, potato slices, green pepper and olives. Drizzle remaining dressing over top; toss to coat all ingredients.
6. Equally divide the salad among 6 plates. Add 1 piece of tuna to each. Divide hard-cooked egg pieces and tomato slices equally among the plates.