In a large pot, bring 12 cups water, Farro and salt to a boil and cook for 25 -30 minutes, until tender. Drain Farro and toss with oil. Spread out on a baking tray and let cool to room temperature.
In a small bowl, combine ingredients and whisk together. Vinaigrette does not need to emulsify. Let rest in refrigerator for at least 30 minutes to combine flavors.
In a large mixing bowl, add Farro, onion, cucumber, salt and vinaigrette. Toss until everything is well coated. Add lettuce and avocados and toss a few more times. Taste and adjust seasoning, if needed. Divide among 8 salad plates and serve.