Place a bell pepper ring in the centre of 4 chilled dinner plates. Artfully arrange orange slices around the bell pepper, and then set plates aside. Combine the balsamic vinegar, orange juice, olive oil, salt and pepper in a salad bowl. Add the salad greens and gently toss to coat. Place salad greens inside the bell rings. Top with flaked tuna. Sprinkle with basil leaves and pine nuts and serve.
Note: To toast pine nuts, place in a single layer in a small baking dish. Bake, shaking the dish from time to time, in a preheated 350 degrees F oven for 10-15 minutes, or until lightly toasted. Cool to room temperature before using.