Heat a large skillet over medium heat with a drizzle of olive oil. Brown the onion and leek over low heat for around ten minutes.
Preheat the oven to 200°. Pre-cook the salmon wrapped in baking paper for 10 minutes.
Once pre-cooked, add it to the onion and leek mixture. Add the double cream, salt, pepper and grated cheese (reserve a little to brown the lasagna). Mix and remove from heat.
Place a spoonful of this preparation at the bottom of the Monbento x Peugeot Saveurs Metal Lunch Box. Add a sheet of lasagna and repeat the operation until the Lunch Box is full. Finish with a layer of leek and salmon mixture then the remaining grated cheese.
Bake in the oven preheated to 180° for 25 to 30 minutes. At the end of cooking, sprinkle with chopped fresh parsley.