Prepare the mashed potato by cooking the potatoes in a large saucepan of boiling, salted water until tender; usually 15-20 minutes. Drain and allow to steam for a few minutes before mashing with the Crème fraîche, butter and seasoning. Cover and reserve until serving point.
Pre-heat the oven to 190°C.
Cut 4 squares of nonstick baking paper roughly 30cm x 30cm in dimension. Place the salmon fillets in the middle, then arrange the asparagus, olives, and lemon zest around and on top of the fish. Drizzle the olive oil on top and season generously. Bring the sides of the baking paper up and around the ingredients to create a parcel.
Place on a large baking tray and bake for 12-15 minutes until the salmon is just cooked; firm yet springy to the touch. As the salmon is cooking, reheat the mashed potato in a microwave.
Remove the salmon and transfer to serving plates. Carefully open up the nonstick baking paper (steam will escape so take care) and serve the mashed potato in bowls on the side.