Heat your oven to 200°C/Fan 180°C/Gas 6. Peel, halve and quarter the sweet potatoes lengthways. Chop them into 2cm-wide chunks. Place in a roasting tin. Drizzle with 1 tbsp olive oil and season. Toss to coat the sweet potatoes in the oil. Slide into the oven. Roast for 35 mins till tender and lightly browned.
While the sweet potatoes roast, roughly chop the tomatoes and place in a separate roasting tin or baking tray. Peel and finely chop the onion and add to the tin with the unpeeled garlic cloves and sprinkle over 2 tsp smoked paprika. Drizzle with 1 tbsp olive oil and 1 tbsp balsamic vinegar. Season with salt and pepper. Toss to mix and coat. Roast below the sweet potatoes for 25 mins till softened.
Take the tomatoes out of the oven after 25 mins. Squeeze the garlic cloves from their skins. Tip everything into a blender (or use a stick blender in the tin) and blitz together. No blender? Squash the garlic cloves, then stir back into the tin and mash with a potato masher for a chunkier sauce.
Pour the tomato sauce over the sweet potatoes and toss to mix. These are your batatas bravas. Cover the tin with foil and set aside to keep warm while you cook the cod.
Heat your grill to high. Place the cod fillets on baking tray or grill pan, skin-side up. Brush them with 1 tsp oil each. Slide under the grill. Cook for 10 mins till the skin is crisp and the cod is opaque and flakes easily when you press it with a fork (you don’t need to turn it over, it will cook through from the top).
While the cod grills, mix another 1 tbsp balsamic vinegar with ½ tbsp olive oil. Pour over the rocket and toss to mix. Finely chop the flat leaf parsley.
Serve the cod with the batatas bravas and a handful of rocket. Scatter over the chopped parsley to garnish.