In a medium bowl, mix together the matzo meal, potato starch, onion powder, garlic powder, baking powder, and salt. Make a well in the center of the dry ingredients and add in the water and oil. Stir to combine. If the mixture is too dry, add more water a tablespoon at a time. The dough should be between soft and firm, and a good consistency for rolling into balls. If it’s too moist, add a bit of matzo meal. Set aside to rest for about 30 minutes. The dough will firm up as it rests. In a large pot, heat oil on medium heat. Add leeks, celery, carrots, shiitake, and salt. Cook for about 5 minutes until vegetables start to soften. Add vegetable broth and bring to boil then reduce to a gentle simmer. Roll dough into about walnut-sized (they will expand when cooked) balls and drop into the soup. Simmer for about 15 minutes. Matzo balls should puff up and float when they are done. Serve immediately with fresh dill as garnish.