How to Make It
In a blender, puree the cilantro, canola oil, garlic, ginger, paprika, salt, turmeric and cumin until smooth. Pour the marinade into a resealable plastic bag, add the salmon and seal the bag. Turn to coat the fish and refrigerate overnight.
In a small skillet, heat the olive oil. Add the mushrooms and garlic and cook over moderately low heat, stirring, until the mushrooms are well browned, 10 minutes. Scrape the mushrooms and garlic into a blender and let cool. Add the tahini, lemon juice and 1/3 cup of water and puree until smooth. Stir in the dill and season with salt.
In a medium saucepan, toast the couscous over moderate heat, tossing, until golden, 10 minutes. Transfer to a small bowl. In the same saucepan, heat the olive oil. Add the onion and a pinch each of cinnamon and salt and cook over moderately low heat, stirring occasionally, until the onion is softened and just starting to brown, about 8 minutes. Add the toasted couscous and cook for 1 minute, stirring, then stir in the tomato puree. Add the warm water 1/2 cup at a time and stir constantly over moderately low heat, allowing the liquid to be absorbed between additions, until the couscous is al dente, about 20 minutes. Season with salt and keep warm; add 1 or 2 tablespoons of water if the couscous seems dry.
Light a grill or preheat a grill pan. Scrape the marinade off the salmon, season the fish with salt and grill over high heat, turning once, until lightly charred and nearly cooked through, 3 to 5 minutes. Spoon the couscous onto plates, top with the salmon, drizzle with the tahini sauce and serve.