These sandwiches highlight wild Alaskan pollock—flavored with aromatic seasonings, coated with panko breadcrumbs, and pan-fried for a golden-brown crust. In classic fashion, a tangy, mayo-based tartar sauce perfectly balances the fish.
Place an oven rack in the center of the oven, then preheat to 450°F. Wash and dry the fresh produce. Cut the sweet potatoes lengthwise into 1-inch-wide wedges. Place on a sheet pan. Drizzle with olive oil and season with salt and pepper; toss to coat. Arrange in an even layer, skin side down. Roast 27 to 29 minutes, or until browned and tender when pierced with a fork. Reserving the sheet pan, transfer to a plate and set aside in a warm place.
While the sweet potatoes roast, cut off and discard the root end of the lettuce; thinly slice the leaves. Halve the rolls. In a bowl, combine the mayonnaise, creamy mustard sauce, and sweet pickle relish. Season with salt and pepper to taste. Pat the fish fillets dry with paper towels. Halve crosswise.
While the sweet potatoes continue to roast, season the halved fish fillets on both sides with salt, pepper, and the spice blend. Crack the eggs into a bowl; season with salt and pepper. Beat until smooth. Place the breadcrumbs on a plate; season with salt and pepper. Working one piece at a time, thoroughly coat the seasoned fillets in the beaten eggs (letting any excess drip off), then in the breadcrumbs (pressing to adhere). Transfer to a separate plate.
While the sweet potatoes continue to roast, in a large pan (nonstick, if you have one), heat a thin layer of oil on medium-high until hot. Once the oil is hot enough that a pinch of breadcrumbs sizzles immediately when added, working in batches if necessary, add the breaded fish fillets. Cook 2 to 3 minutes per side, or until browned and cooked through. (If the pan seems dry, add 1 teaspoon of olive oil before flipping.) Transfer to a paper towel- lined plate; immediately season with salt and pepper.
While the fish cooks, place the rolls on the same sheet pan, cut side up. Drizzle with olive oil. Toast in the oven 4 to 5 minutes, or until lightly browned. Transfer to a clean work surface.
Divide the sauce, cooked fish fillets, and sliced lettuce among the toasted rolls. Serve the sandwiches with the roasted sweet potatoes on the side. Enjoy!