Sprinkle the halibut with salt and pepper. Lay 2 slices of prosciutto on a flat surface, slightly overlapping each other. Place a halibut fillet at the end of the slices and roll up (like a mini burrito). Repeat with the remaining prosciutto and halibut.
Heat the oil in a large ovenproof skillet over medium-high heat. Sear the halibut just until the prosciutto gets browned, about 1 minute per side. (If your pan is hot enough, this will happen quickly. This is just for color and crisping the prosciutto; the fish will cook later in the oven!) Transfer the fish to a plate.
Quickly stir the garlic, lemon zest and chile flakes into the skillet. Add the Brussels sprouts and kale and saute until tender, 7 to 8 minutes. Season with salt and pepper. Stir in the couscous, hot stock and currants. Place the fish on top of the mixture and transfer to the oven. Bake for 8 minutes. Remove the fish from the skillet, fluff the couscous with a fork and serve.