You can find dried porcini mushrooms at Whole Foods. They are about nine dollars for a one-ounce bag, which sounds really expensive, but it's not. That bag will last you quite a while. I use them all the time, and that tiny bag lasts about five months. They are great in stocks, soups, stews, and veggie burgers.
Porcini Mushroom Veggie Burger
(Makes 4 veggie burger patties)
1 8-oz. package of tempeh (crumbled)
1 1/2 cups portobello mushrooms (diced)
1 tablespoon dried porcini (minced)
1 cup smoked provolone cheese (shredded)
1/2 cup shallot (minced)
1/2 teaspoon sea salt
1/2 teaspoon garlic powder
1 teaspoon vegetarian worcestershire sauce
cracked black pepper (to taste)
1 tablespoon Creole mustard
1 tablespoon tomato paste
2 eggs
1/4 cup flour
1/4 cup of oil for frying

Once you have all of your toppings ready, preheat your outdoor grill to 500 degrees. Cook burger patties for about 3-4 minutes per side or until well-marked by the grill grates and heated through. Serve on a soft sesame bun with romaine lettuce, sliced tomato, pickles, thinly sliced shallot, mustard, and mayonnaise.