In a small bowl, combine all the vinaigrette ingredients and whisk until thoroughly emulsified (it will look creamy).

In a large mixing bowl, combine the lettuce, parsley, endive, and scallions. Gently toss the greens thoroughly with about 2 tablespoons of the vinaigrette. Mound the greens onto four salad plates (white looks nice), arranging any endive and parsley pieces that have fallen to the bottom of the bowl on top.

Cut the avocado in half and remove the pit. Slide a large spoon between the skin and flesh to peel each half. Slice the avocado halves crosswise in very thin half-moons (1/8 inch thick).

With the flat side of a chef's knife, transfer the avocado halves to the mixing bowl, fan them out slightly, drizzle over another 1 tablespoon of the vinaigrette, and gently toss just to coat the avocado, keeping the slices somewhat together. Arrange a little pile of avocado slices on one quarter of the salad, propped up against the mound of leaves. Drizzle the whole salad with a tiny bit more vinaigrette and serve right away.