Prepare the Avocado Grapefruit Dijon Vinaigrette. In a small bowl, whisk together the shallot, vinegar, juice, and mustard. Whisk in the oil in a slow stream to emulsify.
Season with salt and pepper. (The Vinaigrette will keep refrigerated in an airtight container for up to a week.)
To serve, toss the lettuce lightly with some of the vinaigrette in a large salad bowl.
Divide among salad plates and top with the herbs and nuts. Just before serving, drizzle a little more vinaigrette and grind some salt and fresh pepper over each.