Prepare the Tartar Sauce:

1. Combine Ingredients: In a small bowl, mix mayonnaise, pickle relish, lemon juice, Dijon mustard, dill, salt, and pepper.
2. Chill: Cover and refrigerate until ready to serve.

Prepare the Fried Cod:

3. Season the Cod: Pat the cod fillets dry and season with salt and pepper on both sides.
4. Set Up Dredging Station: In three shallow bowls, place flour in one, beaten eggs in the second, and a mixture of panko breadcrumbs, cornmeal, garlic powder, paprika, and cayenne in the third.
5. Coat the Fish: Dip each fillet into the flour, shaking off excess, then into the beaten eggs, and finally into the breadcrumb mixture, pressing gently to adhere.
6. Heat the Oil: In a large skillet, heat vegetable oil over medium-high heat until shimmering (around 350°F).
7. Fry the Fish: Fry the fillets in batches for 3-4 minutes per side or until golden brown and cooked through. Transfer to a wire rack or paper towel-lined plate to drain.

Assemble the Sandwiches:

8. Toast the Buns: Lightly toast the sandwich buns for added texture and flavor.
9. Layer the Ingredients: Spread tartar sauce on the bottom bun, add lettuce, a fried cod fillet, tomato slices, onion rings, and cheese if using. Top with the bun lid.

Serve:

10. Serve immediately with your favorite sides, such as fries, coleslaw, or a fresh salad.