Halve any larger potatoes, then cook in a large pan of boiling salted water for 15 minutes, or until cooked through. Drain in a colander and leave to steam dry.
Once they’re cool enough to handle, slice them 1cm thick and place in a large roasting tray. Drizzle over a little oil, then finely grate over the lemon zest. Chop and scatter over half the dill, then season with a pinch of sea salt and pepper black.
Toss to coat, then lay the dab fillets on top and scatter over the prawns.
Coarsely grate the Cheddar. In a bowl, mix the yoghurt, half the Cheddar and the mustard. Finely chop the remaining dill and add most of it to the bowl, then squeeze in the juice of half a lemon and mix again.
Snap off the woody ends, then use a speed-peeler to peel the asparagus into long strips. Gently fold them into the yoghurt dressing.
Top each piece of dab with some of the dressed asparagus then pour over any leftover yoghurt dressing and sprinkle over the remaining Cheddar.
Bake in the oven for 20 minutes, or until everything is slightly browned on top and the fish is beautifully cooked through.