Place an oven rack in the center of the oven, then preheat to 450°F. Wash and dry the fresh produce. On a paper towel-lined cutting board, cut the potatoes into 1-inch-wide wedges. Line a sheet pan with foil. Place the potato wedges on the foil. Drizzle with 1/2 teaspoon of olive oil and season with salt, pepper, and the Italian seasoning; toss to coat. Arrange in an even layer, skin side down, on one side of the sheet pan. Roast 13 minutes. Leaving the oven on, remove from the oven. 

Meanwhile, cut out and discard the core of the cabbage; thinly slice the leaves. Peel 1 clove of garlic; using a zester, finely grate into a paste (or use the small side of a box grater). Quarter and deseed the lemon. In a large bowl, whisk together the mayonnaise, the juice of 2 lemon wedges, and 1/2 teaspoon of olive oil. Add the sliced cabbage; season with salt and pepper. Toss to coat. Set aside to marinate, stirring occasionally, at least 10 minutes. Taste, then season with salt and pepper if desired. 

Meanwhile, in a bowl, combine the breadcrumbs, parmesan, garlic paste, the juice of the remaining lemon wedges, and 1/4 teaspoon of olive oil. Season with salt and pepper. 

Pat the fish dry with paper towels. Transfer to a plate. Drizzle with 1/4 teaspoon of olive oil and season with salt and pepper; turn to coat. Carefully transfer to the other side of the sheet pan of partially roasted potatoes. Evenly spread or brush the mustard onto the fish, then carefully top with the breadcrumb topping (pressing to adhere). Roast 8 to 10 minutes, or until the potatoes are tender when pierced with a fork and the fish is cooked through.* Remove from the oven. Serve the roasted fish and potatoes with the slaw. Enjoy!

* An instant-read thermometer should register 145°F.