1. Combine all dressing ingredients in a blender. Blend well, scraping down sides of blender several times to incorporate all ingredients; reserve.
2. Combine quinoa with 2 cups water in a medium saucepan; bring to a simmer. Cook, covered, over low heat, until water has been absorbed and quinoa is tender (about 12 minutes); reserve.
3. Cook the sausages in a skillet with 1/4-inch water, over medium heat, turning occasionally. Continue cooking until the water evaporates and sausages brown slightly (about 10 minutes); transfer to a cutting board, and slice into 1-inch pieces.
4. Scatter the quinoa over a large platter. Arrange salad greens, tomatoes, onion, and sausages over quinoa; drizzle with the reserved dressing. Sprinkle salad with tarragon, chives, and a final dash of coarse black pepper.