Cut the potatoes into cubes and cook in a saucepan of boiling water until tender. Drain and mash with a little milk. Set aside.
In a medium saucepan, melt the butter and stir in the flour. Slowly add the milk while stirring to prevent lumps. When all the milk has been added and the sauce begins to thicken, add the paprika, frozen vegetables, fish and parsley. Season with salt and pepper.
Pour the filling into a 6-8 cup capacity ovenproof dish and top with mashed potatoes.
Cook in the preheated oven for 30 minutes or until heated through and the top is golden.
If using the cheese, sprinkle over the potatoes and place under the grill on high heat for 2-3 minutes or until it browns.
Try this fish pie with salmon pieces or canned smoked fish.