Preheat oven to 400°F. Line a rimmed baking sheet with aluminum foil and coat lightly with nonstick spray (or use parchment paper).
Place salmon skin-side down on the prepared pan. Pat dry, then brush the top of each piece of salmon with olive oil. Season each fillet with about ¼ teaspoon of Old Bay.
Roast in the oven for 8-11 minutes, or until the fish flakes easily with a fork.
Meanwhile, spread butter on each half of the sandwich buns. Toast in a cast iron skillet or on a griddle over medium heat until golden brown, about 3-4 minutes.
Serve each salmon fillet on a toasted roll with lettuce, tomato, pickles and tartar sauce.
MAKE THE TARTAR SAUCE (OR USE STORE-BOUGHT):
Stir together all ingredients. Season with salt and pepper, to taste. Cover and refrigerate until ready to serve.
Notes
To achieve a crisp exterior, transfer the salmon to the broiler at about the 8-minute mark. Broil for a couple more minutes, until the top is nicely browned and the salmon is cooked through.
How to Bake a Juicy Salmon for Sandwiches: The total baking time will vary depending on the size and thickness of your fillets. You know the fish is done when it flakes easily with a fork. Be careful not to overcook the salmon or it will become dry.
Use fresh salmon or frozen salmon for this recipe. If starting with frozen salmon, make sure that it's completely thawed before using. You can thaw salmon in the refrigerator overnight or quickly thaw it by placing the salmon in a large Ziploc bag and submerging it in a bowl of cold water.
Skin-on salmon works best because the skin provides a safety layer between the fish's flesh and the hot pan, helping the salmon retain its juices and cook evenly. In a pinch, you can certainly use salmon with the skin already removed.
Garnish the fish with a squeeze of fresh lemon juice before assembling the sandwiches for a bright, acidic note.