In a medium size saucepan, bring the chicken stock, scallions, garlic and butter to a boil. Stir in the couscous and season with salt, pepper, dill and lemon juice. Turn off the heat, cover the pot and let stand for 5 minutes, then fluff with a fork.
Meanwhile, heat a drizzle of EVOO in a nonstick skillet over medium-high heat. Season the salmon with the cumin, coriander, salt and pepper. Add to the skillet and cook the fish for 2 minutes on each side for medium-rare doneness (for fish that is opaque and cooked through, add a minute on each side).
Serve the fish with the couscous alongside and a generous dollop of yogurt on top.