Preheat the oven to 350 degrees F. Cook the orzo in boiling water until just tender, about 7 to 8 minutes. Drain well, cool in ice-cold water, and drain well again. Brush an 8” x 8” baking dish with 1 Tbsp. of oil. Place the orzo in the dish; mix in the tomatoes, olives, cheese, salt and pepper. Pour in the stock. Cover and bake 30 minutes, or until heated through and the tomatoes are softened.
When the orzo is about 15 minutes from being done, preheat your grill to high. Cut the tuna into 4 long strips of equal width. Brush the tuna with 2 Tbsp. of olive oil. Set the herbs on a wide plate. Lightly oil the bars of the grill. Grill the tuna about 30 seconds per side, until nicely grilled on the outside, but still rare in the middle. Set the tuna on the herbs and gently turn to coat. Divide the orzo among 4 shallow bowls. Slice the tuna and artfully arrange on top of the orzo. Drizzle with a little olive oil. Garnish each serving with a parsley or oregano sprig and serve.