While the oven is heating, bring the beef to room temperature, and make the balsamic dressing: Place the balsamic vinegar, port and brown sugar in a medium-sized sized saucepan, and stir. Bring to the boil, then immediately reduce heat, and simmer until reduced to less than 1 cup of syrup. Cool.
Rub the beef with olive oil, and season with salt and pepper. Tie it with kitchen string so that it retains its shape.
Heat a heavy, preferably non-stick skillet, and seal the meat on all sides.
Place seared beef on a baking tray and roast in the oven for 15 minutes, or longer to your preference. Allow it to rest, in a warm place, for 30 minutes.
While the oven is still on and the meat is resting, place the bread on a baking tray, drizzle or brush with olive oil, and bake until golden. Cool.
Meanwhile prepare the salad: Blanch the beans in boiling salted water for 2 to 3 minutes, until barely cooked. They should remain crisp. Refresh in hot water immediately, then drain. Peel and slice the roasted red bell peppers into bite-sized pieces. Skin, seed and dice the tomatoes.
Slice beef and transfer it to a suitable-sized serving bowl, along with the juices.
Add the salad ingredients - beans, bell peppers, tomatoes, parsley, salad greens, and bread - and mix together gently.