Combine the bulgur and broth or water in a medium bowl. Cover and let sit for at least 90 minutes at room temperature, or refrigerate overnight. (If using whole-wheat couscous, it will be ready after about 45 minutes but can also refrigerate overnight.) When ready to serve, fluff the bulgur with a fork. Add the chickpeas, cucumber, tomatoes and scallion, and toss to incorporate.
Whisk together the miso, sesame oil, vinegar, vegetable oil and honey in a medium bowl. Pour all but 2 Tbsp. over the bulgur mixture and toss to incorporate.
Divide the watercress leaves among salad plates or bowls. Drizzle with the remaining dressing. Mound some of the bulgur mixture on top of each portion, add the avocado and serve.