1. Add wheat berries to a medium pot and fill with water. Cover and bring to a boil. Reduce to a simmer and cook for 15 minutes, until tender. Drain.
2. Meanwhile, heat a grill or grill pan to medium-high. Whisk 3 tbsp of the vinegar, 2 tbsp of the oil, the mustard, 1/4 tsp of the salt and 1/8 tsp of the pepper. Pour half the vinaigrette over kale leaves and toss well. Brush remaining vinaigrette over mushrooms (skewer cremini, if desired). Grill cremini for 4 minutes per side and shiitakes for 2 minutes per side, turning each once. Grill kale for 2 minutes per side, in 2 batches. Quarter cremini, slice shiitakes and chop kale, discarding stems on the latter. Stir into cooked wheat berries with walnuts and remaining 2 tbsp vinegar, 1 tbsp oil, 3/4 tsp salt and 1/4 tsp pepper. Top each serving with a poached egg, if desired.