Preheat oven to 180°C fan bake. Melt the butter in a saucepan. Add the onion and cook over a medium heat until soft but not brown. Pour in HEINZ [SERIOUSLY] GOOD™ Four Cheeses Creamy Lasagne Bake and stir until nearly boiling. Remove from heat and stir in grated lemon zest, parsley, salmon, fish and prawns. Carefully mix to combine. Spoon into an ovenproof dish. Top with the potato and kumara mash, and sprinkle over grated Parmesan cheese.