Pre-heat the grill to medium. Cook the new potatoes in boiling, salted water until they are tender, then drain and set them aside.
Put the packet of spinach in the microwave and cook for 4 mins until wilted. Squeeze the water out of the spinach and roughly chop. Add the cheese and a little grated nutmeg if you like, then season well.
Put fish fillets in a baking dish with a little olive oil. Divide the spinach mixture into 4 and place on top of each fillet. Sprinkle over the breadcrumbs and grill for 10-12 mins.
Lightly crush the potatoes with the back of a fork and stir through some olive oil and the chopped parsley, then serve with the fish.
Notes
For extra flavour, try substituting half the breadcrumbs for Parmesan.