Bring water, white wine, lemon juice and seafood seasoning to a gentle boil in a 3-qt. sauté pan. Reduce the heat and simmer for 15 minutes.
Lay the scallions across the bottom of the pan in the poaching liquid and place the salmon filets on top. Cover and poach for 8 - 10 minutes.
Discard the scallions and place the salmon on warmed plates.
Increase the heat on the poaching liquid and reduce the volume of the liquid by one half.
Separately, with a fork, combine the butter and flour to make a paste (this is called beurre manie). Add the beurre manie to the reduced liquid and allow to thicken. Drizzle some of the sauce over each of the salmon steaks.
Garnish with some minced parsley and a lemon slice or two.