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.
Notes
If you make a nice-sized batch of wheat berries early in the week you can throw them into all kinds of side dishes and salads for extra texture (true of most grains). They kind of remind me of barley, but with even a bit more chew.