Preheat the oven to 230C / fan 210C.

Cut the potatoes into 2cm chunks. Place on a large, lined baking tray and drizzle with 1 tbsp oil; season with sea salt and black pepper. Roast for 25-30 mins, until beginning to soften.

Finely slice the onions. Heat a medium frying pan with 1 tbsp oil on a medium-low heat and add the onions. Season with sea salt and cook for 15-20 mins, stirring occasionally, until caramelised.

Meanwhile, quarter the lettuces lengthways. Heat a large frying pan with 1/2 tbsp oil on high heat. Add the lettuce, season with sea salt and cook for 1 min per side, until blackened. Roughly chop and set aside.

Remove the tarragon leaves from their stalks and finely chop. Finely slice the chives. In a large bowl stir the herbs with the yoghurt and half the mustard dressing. Season with sea salt and black pepper.

Push the potatoes to one side of the tray. Place the sole, skin-side down, on the tray. Zest the lemon over the sole and drizzle with 1/2 tbsp oil. Scatter the capers over the top and bake for 7-8 mins, until cooked through.

Toss the potatoes with the herby yoghurt and add a squeeze of lemon juice (to taste). Halve the tomatoes and add to the bowl with the lettuce, along with some caramelised onions; drizzle over the remaining dressing. Serve the sole with the lettuce salad, potato salad and remaining caramelised onions.

Healthy dinner recipes: baked sole and potato salad is perfect for post-workout