Lay the three slices of pancetta, slightly overlapping each other, on a chopping board. Place the fish in the middle, across the pancetta, and then bring the slices up towards the middle to wrap the fish.
Heat the olive oil in a chargrill pan and fry the fish for 2-3 minutes on both sides, or until the pancetta is crisp and the fish is cooked through.
Press the boiled sweet potato through a potato ricer into a mixing bowl and stir in the butter. Mix in the flour until well-combined and smooth, then shape into patties using your hands. Fry in the same pan as the fish for 2-3 minutes on both sides, or until golden-brown and crisp all over.
To serve, place the sweet potato cakes on a serving plate and place the fish on top. Garnish with fresh basil leaves.