For dressing: Mix together vinegar and mustard. Slowly add olive oil while whisking the dressing. Add salt and pepper to taste. Adjust vinegar and oil to taste, the dressing shouldn't be too heavy or oily.
In a large bowl, mix the cooked farro and vegetables together, including shallots. Add the lemon zest and basil, then the dressing and mix thoroughly. Add the feta last. Garnish with fresh basil. Don't overdress or the salad will be heavy.