Place the wheat berries in a large mixing bowl, and add the tomatoes, onion, olives, scallions, parsley and mint. Toss to combine.
In a small bowl, or a container place the olive oil, thyme, lemon juice, rice vinegar, mustard, and salt and pepper. Stir or shake to combine well, then pour the dressing over the grain salad. Toss to combine. Transfer to a serving bowl and serve at room temperature.