Rinse the cod and pat dry with paper towels. Cut the filets into 3-inch pieces. Season the pieces on both sides with freshly ground pepper and some salt.
Cut the asparagus into 2-inch pieces.
Place the flour in a shallow bowl.
Heat 2 Tbs olive oil in a large skillet. Working in batches, coat the cod in flour. When oil is hot, add the pieces of cod and sear until golden, about 1 minute per side. Transfer the cod to a plate.
In the same skillet, add the remaining olive oil and the butter. When it starts foaming, add the asparagus and cook, stirring once in a while, for 3 to 4 minutes. Add the minced garlic and cook for 1 minute. Add the preserved lemons and stir. Then add the stock. Bring to a boil and cook for about 2 minutes.
Return the cod pieces and any collected juices to the pan and arrange with the asparagus. Cook on low heat for about 2 minutes, until the sauce is slightly reduced and the cod is warmed through.
Sprinkle with fresh minced garlic and serve over couscous.
Make the couscous
In a stockpot, add 1 1/4 cups water, 2 Tbs olive oil, 1 minced garlic and 1/2 Tbs minced parsley. Bring to a boil and add 1 cup couscous. Cover and remove the pan from the heat source. The couscous will absorb all the liquid. Before serving fluff it with a fork.
Serve the fish and asparagus over a few spoonfuls of couscous.