Adjust rack to top position and preheat oven to 425 degrees. Wash and dry produce.

Cut potatoes into ½-inch-thick wedges. Trim and thinly slice scallions, separating whites from greens; roughly chop whites. Quarter lemon. Trim and halve mushrooms (quarter any larger mushrooms; skip if your mushrooms are pre-sliced!).

Toss potatoes on a baking sheet with a large drizzle of oil, half the Old Bay Seasoning (you’ll use the rest later), salt, and pepper. Roast on top rack, flipping halfway through, until browned and tender, 20-25 minutes.

In a medium bowl, combine cabbage, scallion greens, sour cream, 1 tsp sugar (2 tsp for 4 servings), and juice from one lemon wedge (two wedges for 4). Season with salt and pepper.

In a second medium bowl, combine mayonnaise, mustard, scallion whites, juice from one lemon wedge (two wedges for 4 servings), and hot sauce to taste.

In a third medium bowl, whisk together tempura batter mix, garlic powder, remaining OId Bay Seasoning, ⅓ cup cold water (⅔ cup for 4), and a big pinch of salt. (TIP: If mixture is too thick, add more water 1 TBSP at a time until it reaches a pancake-batter-like consistency.) Stir mushrooms into batter until fully coated.

Heat a ⅓-inch layer of oil in a large pan over medium-high heat. Once oil is hot enough that a drop of batter sizzles when added to the pan, use tongs to add coated mushrooms in a single layer. TIP: Work in batches if necessary.

Cook until golden brown, 3-4 minutes on first side and 1-2 minutes on second side. Using a slotted spoon, transfer mushrooms to a paper-towel-lined plate. Season with salt.

While mushrooms cook, halve baguettes lengthwise, stopping before you get all the way through.

Toast, cut sides up (place directly on oven rack or use a baking sheet), until golden brown, 3-5 minutes.

Spread cut sides of baguettes with spicy remoulade; fill with mushrooms, pickle slices, and as much slaw as you like.

Divide sandwiches and fries between plates. Serve with any remaining slaw, any remaining remoulade, and remaining lemon wedges on the side. TIP: If you’ve got some on hand, serve ketchup or malt vinegar with your fries!