Pour all the oil from the jar of peppers into a deep frying pan. Heat the oil until bubbling, then tip in the potatoes and onion and toss in the oil. Cook for 5 mins, stirring every now and then until the potatoes are beginning to turn golden.
Carefully pour most of the oil out of the frying pan, leaving behind about 1 tbsp. Tip in the beans and drained peppers, season and stir until well mixed. Lay the fish, skin side down, on top of the vegetables.
Cover the pan and cook over a medium heat for 5 mins more or until the fish flakes easily with a fork and the vegetables are tender. Squeeze the lemon half over the fish and serve with crusty bread to mop up the juices.
