Cut the bell peppers in half lengthwise, remove the stems and seeds, and chop into bite-sized pieces.

Pat the yellowtail fillets dry with a paper towel, cut into bite-sized pieces, season with salt and pepper, and coat with cornstarch, shaking off excess powder.

Heat salad oil in a frying pan over medium-low heat, add the yellowtail, and fry until golden brown on both sides. Add the bell peppers and stir-fry until lightly coated with oil.