How to Make It
In a medium saucepan, combine the vinegar, honey, mustard seeds, salt and 1 cup of water and bring to a simmer over moderate heat. In a medium heatproof bowl, cover the tomato slices with the hot brine. Let cool completely, then cover and refrigerate the tomatoes overnight.
In a medium bowl, cover the bulgur with 2 cups of water and let stand until the grains are plumped and tender, about 1 hour; drain the bulgur well.
Meanwhile, in a medium skillet, toast the walnuts over moderate heat, stirring, until golden, about 5 minutes. Let cool, then finely chop the nuts.
Drain the green tomatoes and cut them into 1/4-inch dice. In a large bowl, toss the bulgur with the pickled tomatoes, chopped walnuts and all of the remaining ingredients. Season the tabbouleh with salt and serve.