Mushroom and Wheat Berry Soup

Name: Mushroom and Wheat Berry Soup
Ingredients: 1 cup wheat berries , rinsed; 3 tablespoons cold-pressed extra-virgin olive oil; 1½ pounds cremini mushrooms , trimmed and sliced thin; Salt and pepper; 1 onion , chopped fine; 6 garlic cloves , minced; 2 teaspoons tomato paste; 1 cup dry sherry; 8 cups homemade or low-sodium chicken or vegetable broth; 1 tablespoon low-sodium soy sauce; 1 sprig fresh thyme; 1 bay leaf; ½ ounce dried shiitake mushrooms , finely ground using spice grinder; 4 ounces mustard greens , stemmed and chopped; ¼ teaspoon grated lemon zest