Using a sharp knife, carefully slice off the skin from the oranges. Cut each orange into ¼-inch thick slices.
Divide baby spring mix evenly between 4 salad plates. Place 4 to 5 slices of oranges, a few blackberries, and some walnuts on top of the spring mix on each plate.
Combine all vinaigrette ingredients in an empty bottle. Put on the lid and give it a good shake until everything is well mixed. Drizzle over fruits and vegetables.
Serve immediately.
Notes
Any leftover vinaigrette should be used within 3 to 4 days.