Using meat mallet, vigouously pound each steak until well tenderized and about 1/8" thick.
In a large bowl, combine 3 cups of flour with 3 tablespoon seasoning salt. In another large bowl, combine buttermilk with remaining 1 tablespoon seasoning salt.
Coat steaks with flour. Shake off excess flour, dip steaks in buttermilk, and then coat again with flour. Place coated steaks on a rack over a sheet tray until ready to fry.
Preheat oven to 200 degrees.
Heat 1/2" of oil in large, deep-skillet or Dutch oven over medium-high heat until almost smoking. Fry the steaks in the hot oil until golden brown and cooked through, 1 to 2 minutes per side.
When steak is done, transfer to paper-lined tray or plate to drain, and keep warm in the oven while you fry the oysters and make the gravy.
Coat oysters with the flour. Shake off excess flour, dip oysters in buttermilk and then coat again with flour. Fry oysters in hot oil until golden brown and cooked through, 2 to 3 minutes. Transfer the oysters to another paper-lined tray and place in the oven. Reserve pan with fond to make the gravy.
Add 2 tablespoons flour to skillet and cook, stirring, with the crumbly bits and oil 3 to 4 minutes. Add the onion, 1/4 cup green onions, salt, pepper and 1/2 teaspoon seasoning salt, and saute until vegetables are tender, about 4 to 5 minutes. Whisk in the milk, a little at a time, until thoroughly combined. Cook until gravy is smooth and thickened, about 5 to 10 minutes.
Spread a large serving spoonful of gravy on serving platter. Top with 4 steaks in spoke-like fashion. Place oysters atop each steak. Spoon additional gravy over oysters and in center of platter. Sprinkle with remaining green onions and serve.