Preheat oven to 400 degrees. Brush each of two rimmed baking sheets with 1/2 tablespoon oil. Place fillets on sheets; season with salt and pepper. Roast until cooked through, 10 to 15 minutes. Let cool completely; pat dry with paper towels. With a fork, flake fish into small pieces.
In a large bowl, combine eggs, mayonnaise, parsley, lemon juice, and horseradish. Fold in fish and 1/2 cup cracker crumbs; season with salt and pepper. Place remaining 1 cup crumbs on a plate. Form 16 cakes, using about 1/4 cup fish mixture for each. Gently dredge cakes in crumbs, pressing to help adhere. (To freeze, see below.)
In a large skillet over medium-high, heat 1 tablespoon oil. Place 8 cakes in skillet; cook until golden brown, 4 to 6 minutes per side. Repeat with remaining tablespoon oil and cakes. Serve with tartar sauce, if desired.
To make homemade cracker crumbs, place 36 saltine crackers in a food processor. Pulse until coarse crumbs form. Makes 1 1/2 cups.