In a blender or food processor, combine the sugar, stevia, vinegar, orange juice, salt, mustard, and onion, and process for 20 seconds. With the blender on high, gradually add the oil in a slow, steady stream. Remove from the blender and stir in the poppy seeds. Set aside or refrigerate until ready to use. Shake well before using on salad.
Mrs. Dash is found in most grocery stores near the spices.