In a medium bowl, combine the coleslaw mix and scallions.
In a small bowl, whisk to combine the mayonnaise, sour cream, lemon juice, sugar, and 1/4 teaspoon of the salt. Add the dressing to the coleslaw and stir to coat. Cover and refrigerate the slaw until you’re ready to serve.
In the bowl of a food processor, combine the crackers, garlic, parsley, the remaining 1/2 teaspoon salt, and the pepper. Pulse until smooth. Pour the crumbs into a wide, shallow bowl.
In another shallow bowl, lightly beat the eggs. Place the bowls of crumbs and eggs side by side to prepare for coating your fish.
Dip both sides of 1 cod filet first in the egg mixture, shaking the fish lightly over the bowl to allow for any excess to drip off, then put the filet into the bowl of crumbs, pressing to coat one side. Flip the filet over and press to coat the other side evenly with the crumbs. Transfer the coated filet to a plate and repeat the process with the remaining 3 filets.
Heat 1 tablespoon of olive oil in a large skillet over medium-high heat. Add 2 of the filets and cook, undisturbed, until the undersides are crisp and lightly golden, 3 to 4 minutes. Flip the filets and cook for 3 minutes. Transfer to a plate and loosely tent the fish with foil to keep warm.
Reduce the heat slightly and add the remaining tablespoon of oil to the skillet. Add the remaining 2 filets and cook, undisturbed, until the undersides are crisp and lightly golden, 3 to 4 minutes. Flip and cook for 3 minutes. Transfer to the plate with the other filets.
To serve, lay the sliced sandwich buns on a clean work surface. Put one cod filet on each of four bun halves, pile each filet with about 3 tablespoons of slaw, and top with the remaining bun halves.