Cook the orzo according to package instructions until al dente. Drain and rinse under cold water to stop the cooking process. Transfer to a large mixing bowl.

Add the thinly sliced asparagus and lettuce to the bowl with the cooked orzo.

In a blender or food processor, combine the parsley, green onions, tarragon, Dijon mustard, mayonnaise, and olive oil. Blend until smooth. Season with salt and pepper to taste. If the dressing is too thick, slowly add water, a little at a time, while blending, until the desired consistency is reached. Adjust seasoning to taste after adding water to ensure seasoning is not diluted.

Pour the prepared dressing over the salad and toss until well combined and evenly coated.

Give the salad a final toss and adjust the seasoning if necessary. Serve cold as a refreshing side dish or a light main course. You can garnish the salad with additional chopped herbs or a sprinkle of Parmesan cheese before serving, if desired.