Preheat the oven to 200C/180C Fan/Gas 6.
Put the potatoes, tomatoes and spring onions in a large roasting tin. Drizzle with olive oil and dot with 1 or 2 tablespoons of the harissa paste. Season with salt and pepper and mix well to coat the potatoes. Bake for 35 minutes.
Meanwhile, to make the salsa, mix the mint with the olive oil and lemon juice. Season with salt and pepper and set aside.
Place the peppers on a large baking tray and bake them for 25 minutes, or until charred on all sides. Remove the hot peppers from the oven, place them in a large bowl and cover with cling film. When cool enough to handle, remove the skins and cores from the peppers and cut into 2cm/1in pieces and set aside.
Lay the sourdough in the baking tray the peppers were cooked in, drizzle with olive oil and season with salt and pepper. Cook in the oven for 5–6 minutes, until just toasted. Set aside.
To make the harissa baked sea bass, spread the remaining harissa all over the sea bass fillets. When the potatoes have had 35 minutes, remove the tray from the oven and lay the coated fillets on top, skin-side up. Return to the oven for 10 minutes or until the fish is cooked through.
To make the dressing, place the ingredients in a food processor and blend until smooth. Season with salt and pepper to taste and set aside.
To make the salad, place the peppers, toasted sourdough, tomatoes, cucumber, onion, radishes, olives and herbs in a large mixing bowl. Pour the dressing over and mix to coat well.
Drizzle the mint salsa over each sea bass fillet and serve with the salad on the side.