Cut the red bell pepper in half vertically, remove the stem and seeds, and chop into bite-sized pieces. Slice the onion thinly.

Pat the cod dry, cut into bite-sized pieces, season with salt and pepper, and coat with all-purpose flour.

Heat salad oil in a frying pan over medium heat, add the cod, and cook until golden brown on one side. Flip and cook through, then remove from the pan.

Wipe the oil from the pan, add butter, and heat. Add the onion and bell pepper, and sauté over medium heat.