To make the vinaigrette, whisk together the vinegar, mustard and oil in a small bowl. Add the other ingredients, and taste for seasoning.
Preheat the B.B.Q. or grill to high.
Trim and wash the leeks, splitting the top 3 inches / 7.5 cm. if necessary to ensure to remove any grit. Blanch the leeks in salted boiling water for about 7 minutes, or until tender. Dry with paper towel squeezing out as much of the water as possible.
Moisten the leeks and onions with a little olive oil, and season with salt and pepper. Set aside. Bring a medium pan of salted water to the boil, gently add the eggs, and cook for 8 minutes. Plunge the eggs into cold water, and when cool enough to handle, peel carefully. Set aside. Trim off any excess fat from the steak, and cut into 3 cm. slices. Season well, then brush with the olive oil.
Cook the steaks on the barbeque or under the grill until well charred on both sides. When quite blackened, the steaks should be rare inside – cook for another 5 minutes for medium, and another 10 for well done. Leave the steaks to rest on a warm plate, covered lightly with foil. Meanwhile, cook the leeks and onions on the barbeque or under the grill for about 5 minutes, or until charred, and tender.
To serve, cut the hard boiled eggs into quarters, lengthwise. Place the salad leaves in the middle of each plate, and surround with the egg, leeks and onions. Slice the steaks into thick pieces and arrange on top of the salad and spoon some of the vinaigrette over. Garnish with chopped parsley and serve at once.