Szechuan Fish Suan Cai Yu

1 fresh fish around 800g to 1000g 1 cup pickled mustard green 4 fresh shitake mushrooms 10 dried pepper flakes or more as needed 5 green onions or 1 scallion (separate the white part and green part) 10 garlic cloves, peeled and sliced 1 inch root ginger 1 teaspoon salt 10 whole Sichuan peppercorn seeds 3 tablespoons cooking oil 4 tablespoons starch 1 teaspoon white pepper powder 2L water or as needed

1 fresh fish around 800g to 1000g 1 cup pickled mustard green 4 fresh shitake mushrooms 10 dried pepper flakes or more as needed 5 green onions or 1 scallion (separate the white part and green part) 10 garlic cloves, peeled and sliced 1 inch root ginger 1 teaspoon salt 10 whole Sichuan peppercorn seeds 3 tablespoons cooking oil 4 tablespoons starch 1 teaspoon white pepper powder 2L water or as needed