In a small bowl, whisk the lemon juice, zest, and sugar until the sugar is dissolved. Slowly whisk in the oil. Season the vinaigrette to taste with salt and pepper.
In a large salad or mixing bowl, gently toss the arugula, prosciutto, avocado, and pears with half of the dressing. Divide among 2 plates, drizzle with a little of the remaining dressing, and serve immediately.
Photo: Scott Phillips