Cook the farro according to the package directions. Allow to cool
While the farro is cooking, mix the tahini, 3 tablespoons water, lemon juice, Dijon mustard, garlic, sea salt, pepper, and ¼ cup cucumber slices together in a high-speed blender or food processor until smooth and creamy. If the mixture is too thick, add another tablespoon of water. Place in the fridge until ready to use.
Use a vegetable peeler to slice the asparagus into thin strips.
In a large bowl, toss the arugula together with the remaining cucumber slices, sliced radishes, feta, and cooked farro. Add the tahini dressing and gently toss until the salad is coated. Top with the toasted walnuts and parsley.