1. Preheat the grill, grease the rack with non-stick spray.
2. Season tuna steak with a dash of salt and pepper. Set aside for 10 minutes.
3. For dressing – in a jar combine lemon juice, olive oil, balsamic vinegar and Dijon mustard.
4. Close the lid of the jar and shake all the ingredients. Reserve 1 tbsp. of the dressing for the fish.
5. In a large salad bowl take spinach, onions, beans, celery, sundried tomatoes and parsley.
6. Drizzle in the remaining dressing over the salad and toss well.
7. Place the tuna steak over grill rack; grill for 10 minutes, in between turn the sides.
8. Cut the tuna into pieces.
9. Place the spinach mixture in a serving plate, top with tuna pieces and drizzle the dressing and serve.