Slice the courgette and aubergine lengthways into 8-10 strips. On an oiled griddle pan, grill the slices until coloured and soft, set aside and drizzle with olive oil and salt.
Pan fry the plum tomatoes until softened and set aside. Cook the potatoes in saled water.
Pour the polenta onto a plate and press the herring fillet flesh side into the polenta to coat. In a hot non-stick pan, fry the fish in 1 tbsp of olive oil, skin side down until lightly crispy. Turn down the heat and turn over. Cook the polenta side until golden brown.
Warm the courgettes, aubergines, plum tomatoes and olives in the oven. Drain the cooked potatoes and gently crush with a fork just to break the skins. Add a spoonful of pesto and 1 tbsp of olive oil to the potatoes.
Arrange the potatoes in piles on your plates, topping with vegetable ribbons, tomotoes and olives. Add the herring fillets alongside the salad and serve.