1 avocado, preferably Hass, cut into 1/2-inch dice
1 pear, peeled, cored, and sliced
In a small frying pan, toast the nuts over moderately low heat, stirring frequently, until golden brown, about 5 minutes. Or toast them in a 350° oven for 5 to 10 minutes.
Put the potato in a medium pot of salted water. Bring to a boil and simmer until tender, about 10 minutes. Drain and set aside.
Meanwhile, in a large glass or stainless-steel bowl, combine one third of the blue cheese with the vinegar, salt, and pepper. Mix thoroughly and then gradually whisk in the oil. Reserve 2 tablespoons of the dressing. Add the romaine to the rest of the dressing and toss. Transfer to a platter or salad bowl.
Toss the watercress with the reserved dressing. Arrange the remaining blue cheese, the watercress, walnuts, potato, onions, avocado, and pear slices on top of the lettuce.
There's only one grape we can think of that can handle blue cheese, walnuts, avocado, and vinegar. Riesling it is, and an off-dry Kabinett from Germany's Mosel is the one you want.