Chop the cod fillets into rough chunks using a knife — chop down into a coarse mince. Do not use a food processor. You want texture, not paste.

In a large bowl, combine the chopped fish, breadcrumbs, beaten egg, mayonnaise, Dijon mustard, minced garlic, green onions, Old Bay, salt, and pepper. Stir gently just until combined. Do not overmix.

Divide the mixture into 4 equal portions and shape into patties about 3/4 inch thick. Place on a plate, cover, and refrigerate for 10 minutes.

While the patties chill, make the tartar sauce: mix mayonnaise, chopped pickles, lemon juice, and capers in a small bowl. Season with salt to taste and set aside.

Heat a skillet (cast iron preferred) over medium-high heat. Add olive oil and let it get hot until a drop of water sizzles on contact.

Carefully place the patties in the skillet. Do not move them. Cook for 4 to 5 minutes until a golden crust forms on the bottom.

Flip the patties once, gently. Cook another 4 to 5 minutes until the inside is completely opaque and the outside is golden brown. Internal temperature should reach 145°F.

Toast the buns cut-side down in a dry pan for about 1 minute until lightly crisped at the edges.

Spread tartar sauce on both sides of each bun. Layer with butter lettuce, tomato, and the cooked fish patty. Squeeze fresh lemon over the top and serve immediately.