Cut the sanma into bite-sized pieces, season both sides with salt and pepper, and let sit for 5 minutes. Pat dry with paper towels and coat with potato starch.

Cut the onion and yellow bell pepper into 3cm pieces. Remove the stems from the cherry tomatoes.

Mix all the sweet and sour sauce ingredients in a bowl.

Heat 1 tbsp of salad oil in a frying pan over medium heat. Add the sanma and cook until both sides are golden brown. Remove from the pan.

Wipe the pan clean, add the remaining 1 tbsp of salad oil, and stir-fry the onion and bell pepper until the onion softens. Remove from the pan.

Wipe the pan clean again, add the sweet and sour sauce mixture, and bring to a boil.