Heat your grill to its highest setting. Halve the red peppers and remove the seeds and white bits. Place onto a foil lined baking tray. Grill for 10-12 mins till the skin is black and blistered. Place into a bowl and cover with cling film.
Turn off the grill and turn the oven on to 180°C/Fan 160°C/Gas 4. Peel the onion and cut into quarters. Place 3 onto a baking tray lined with baking paper and finely slice the remaining quarter. Set the sliced onion to one side.
Peel the blackened skin from the peppers. Pop the unpeeled garlic cloves and peppers on the baking tray with the onions. Drizzle with 1 tbsp olive oil.
Place in the oven and cook for 15 mins till the garlic cloves are soft. Squeeze the garlic cloves from their skins and tip into a food processor with the peppers, onion and 1 tbsp of red wine vinegar. Blitz till smooth.
Heat 1 tbsp olive oil in a large frying pan. Add the reserved onion slices. Cook for 2 mins till just soft. Pod the broad beans and tip them into the pan. Stir for 1 min. Drain the butter beans and add them to the pan. Cook for 2 mins. Turn off the heat. Pour in 1 tbsp of the red wine vinegar and season.
Pop the beans in a bowl and cover to keep warm. Place the pan back on the heat. Heat 1 tbsp olive oil and add the hake fillets. Cook for 3-4 mins on each side till just cooked through. Remove from the pan and cover to keep warm. Pour the red pepper sauce into the pan. Taste and adjust the seasoning if it needs it. Gently warm through for 1-2 mins.
Toss the rocket through the bean salad. Pile on to two plates. Place a hake fillet on each plate and pour over the roasted red pepper sauce.