In a medium saucepan, place the lentils, one halved onion, a clove of garlic, one bay leaf and enough cold water to cover the lentils by 2 inches. Bring to a boil and reduce to a simmer. Cook lentils for 15-20 minutes, or until tender. Remove onion, garlic and bay, drain and set aside.
While the lentils are cooking, cook the farro. Add the farro and the remaining onion, garlic and bay leaf to a medium saucepan. Cover the farro with cold water by 2 inches and bring to a boil over medium high heat. Reduce to a simmer and cook 20-25 minutes, or until farro is tender (yet still retains a toothsome bite). Remove onion, garlic and bay, drain and set aside.
In a large bowl, whisk together the lemon juice, olive oil, chopped scallions, mint and parsley. Add reserved lentils and farro as well as radishes and toss to combine. Season the salad with salt and pepper to taste. Serve warm or at room temperature.