Blanch green beans for 2½ min, then emerge in ice water until cold. Drain and set aside, sprinkle some sea salt, optional.
In a mixing bowl, add shrimp and shrimp marinade and toss gently and set aside for 5min.
Bring a nonstick skillet to high heat. Once hot, add 3-4 Tbsp olive oil. Quickly add potato starch into the shrimp and message it gently. Drop it into the pan one by one, making sure there's space, to prevent sticking to each other. Cook about 4 min on each side or until golden brown. Plate shrimp to rest.
Lower heat to medium high. Add scallion, green beans and 1-2 Tbsp oil and scorch the beans for about 2min. Add mirin, salt and pepper and give it a stir. Turn off heat and rest on pan for 1min.
Plate the green beans, then shrimp on top. Garnish with sesame seeds and scallions.
Can serve with rice.