Preheat oven to 400°F.

Par-boil potatoes (see headnote): Add potato slices to a medium pot and cover with water. Add a generous pinch of salt to the water. Bring to a boil and cook for 3 minutes. Drain potatoes in a strainer and run cold water over them. Return the pot to the stovetop — you’ll make rice in it so you don’t have to wash it.

Make Fish Wraps: You’ll need one 15-by-13-inch piece of parchment paper or aluminum foil per filet. In the center of each piece of parchment, lay out a “bed” of sweet potato slices, overlapping slightly, then top with a handful of spinach leaves. Drizzle each with 1 tablespoon of olive oil, salt and pepper, then top each vegetable pile with a piece of fish.

On top of each fish, add the shallot (divided evenly), 2 lime slices, and ginger slices (divided evenly), salt and pepper, another tablespoon of olive oil, and a few dashes of sesame oil. Lift up the sides of the parchment paper until they meet above the fish. Turn down a few times and fold the ends under the fish — picture the way the deli guy wraps a sandwich — creating a seal so the steam doesn’t escape. Place the presents onto a cookie sheet, and bake for 20 minutes. (It’s hard to overcook the fish when steaming it like this.)

Make Rice: Rinse rice in a strainer then prepare rice in the medium pot according to package directions. When finished, add salt to taste, and squeeze in juice from the remaining lime half. Toss.

Make Sauce: To a small saucepan set over medium-low heat, add coconut milk, curry paste, peanut butter, salt, brown sugar, and vinegar. Stir gently until everything warms and becomes integrated, 1 to 2 minutes. Remove from heat and set aside until ready to use. (It does not have to be warm when serving.)

Serve: Remove the fish packets from the oven, and open very carefully. (The steam will be hot.) Slide the contents of the packet onto dinner plates (and drizzle any jus that has collected in the packet) alongside a few scoops of rice and, using a fork, remove the lime and ginger slices to the side. Drizzle everything with two or three spoonfuls of coconut-curry sauce — be judicious, it’s delicious but a little goes a long way. Garnish with chiles, cilantro, or chives if using.