Ask the fishmonger to cut and debone the carp fillet, leaving the skin on. Grease an earthenware roasting dish with olive oil. Lightly crush the 4 garlic cloves and place them in the dish. Clean the spring onions, remove the outermost layer, trim about half of the green part, cut in half lengthways, and distribute in the dish.
Rub the carp fillets well with adobo powder or a mixture of cumin and oregano. Season with salt and pepper. Place in the roasting dish. Roughly cut the mushrooms into halves or thirds and distribute in the dish. Place fresh basil on each fillet, then drape a slice of Serrano ham over each. Drizzle with lemon juice and olive oil. Roast at 190°C (374°F) for 15-20 minutes, depending on fillet thickness.
While the fish roasts, cook the pasta in salted boiling water until al dente.
Serving option 1: Place the cooked pasta on plates and arrange the fish fillets and roasted vegetables on top.
Serving option 2: Toss the cooked pasta with a small amount of olive oil and place on plates. Arrange the fish fillets and Serrano ham on top, and arrange the roasted vegetables around the dish. Deglaze the roasting dish with lemon juice, Madeira, and water. Season to taste, stir in milk to thicken, reduce for 2-3 minutes, and pour over the finished dish.