Toast walnuts on a baking sheet in a preheated 350 degrees F oven for approximately 8 minutes, until they smell fragrant. Remove from pan to cool. Wash and dry the greens. Chop chickweed into ½-inch pieces, and tear lettuce into large pieces, keeping smaller leaves whole. Using a sharp knife, remove the peel and white pith from the orange. Slice the orange crosswise into thin sections, and then cut each section into quarters. Peel and slice the avocado into ¼-inch thick pieces. Place chickweed, lettuce, avocado, orange, and walnuts in a large salad bowl and crumble cheese onto salad. Pour vinaigrette over salad, and toss gently.
Combine everything but the oil in a small bowl. Add the oil gradually, whisking with a wire whisk. Taste, and adjust salt and lemon.