Lightly season salmon with salt, pepper and olive oil. Bake @ 450 degrees just until done. Set aside to cool.
In the meantime, heat olive oil over medium heat and add chopped leeks. Saute for several minutes then add garlic, continue to saute until leeks begin to soften. Add the mushrooms, cook until all ingredients are combined. Add the malt vinegar and parsley; cook through. Remove from the heat.
To make the sauce:
Melt the butter, dill & old bay seasoning. Add the flour and cook and stir over medium-low heat for 1 minute. Add the cream, bring to a low boil and simmer until thickened. Add the cheese, stir over low heat until melted. Remove from heat.
Combine flaked cooked salmon, leek mixture and 3/4 of the sauce. Check for seasoning; add salt & pepper if necessary. Stuff cooked shells with mixture and place into a lightly greased dish or dishes of choice. Top with some of the remaining sauce and bake, covered @ 350 degrees for 15 minutes. Remove the covering, top with freshly ground pepper, finely grated mushroom and chopped parsley. Bake, uncovered, for another 10 minutes until bubbly and delicious.