1) Preheat the oven to 180C/Gas 4.
2) Wash the sweet potatoes and place in a deep saucepan with cold water to cover. Bring to a boil and cook until tender. Remove from the heat, drain and allow to cool enough to handle. Peel off the skin, slice into 1 1/3cm pieces and set aside.
3) Place the bay scallops in a medium bowl and toss gently with the lime juice. Cover the bowl with clingfilm and refrigerate for at least 30 minutes and up to 1 hour.
4) Place the coconut on a rimmed baking sheet and toast until golden brown, about 5 minutes, stirring every few minutes so that it toasts evenly. Set aside.
5) Drain the scallops and transfer to a clean bowl. Add the onions, jalapenos, sultanas, toasted coconut, coconut milk, chopped coriander, oregano, and salt and pepper, to taste. Mix well and refrigerate for at least 30 minutes and up to 3 hours.
Sprinkle the salad with coriander leaves and the reserved toasted coconut and serve with Canchita on the side.
Canchita, the un-popped popcorn of Peru:
1) Heat the rapeseed or vegetable oil in a large pot over medium-high heat for 2 minutes. Add the chulpe corn, cover the pot and reduce the heat to medium. Once you hear the kernels pop (like popcorn), shake the pot vigorously to prevent the kernels on the bottom from burning.
2) Once the popping slows, after about 8-10 minutes, drain the canchita in a strainer and rub with a paper towel to remove excess oil. Season with salt while the corn is still warm and serve with the scallop ceviche.