Adjust rack to top position and preheat oven to 450 degrees. Wash and dry all produce. Cut potatoes into 1/2-inch-thick wedges. Toss on a baking sheet with a large drizzle of oil, half the Fry Seasoning (you’ll use the rest in step 4), salt, and pepper. Roast until golden brown, 20-25 minutes.

While potatoes roast, halve, core, and thinly slice apple. Quarter lemon. In a large bowl, toss apple slices with juice from half the lemon. Set aside.

In a small bowl, combine sour cream and mayonnaise. Stir in half the horseradish powder (use all for 4 servings) and a small squeeze of lemon juice. Taste and add more lemon juice if desired. Season with salt and pepper.

Pat barramundi dry with paper towels. Season all over with salt and pepper. Season flesh sides with remaining Fry Seasoning. Heat a large drizzle of oil in a large pan over medium-high heat. Add barramundi skin sides down. Cook until skin is crispy, 4-5 minutes. Flip and cook until fish is opaque and cooked through, 2-3 minutes more.

Add mixed greens to bowl with marinated apple slices. Season with salt and pepper. Toss with a drizzle of olive oil.

Divide potatoes, salad, and barramundi between plates. Drizzle a small amount of horseradish sauce over fish and serve the rest on the side for dipping. Serve with any remaining lemon wedges on the side.