For the fish: Preheat the oven to 400 degrees F.
Place the fish on the shiny side of a large sheet of tin foil, sprinkle with a pinch of salt and pepper and drizzle with the olive oil. Wrap tightly and bake until the fish is just cooked through, 10 to 12 minutes. Set aside to cool. Raise the oven temperature to 425 degrees F for the frikkadels.
Meanwhile, halve the sweet potatoes and boil them in their skins until soft, 15 minutes, adding the peas for the last 2 minutes. Drain the potatoes and peas. Allow the potatoes to cool and steam for a few minutes and then remove the potato skins. Season with salt and pepper, and mash roughly. (Alternatively, steam or bake the potatoes in their jackets.)
Flake the fish into a bowl, then add in the mashed potato and peas and the cilantro, mint, lemon juice, lemon zest, cumin, coriander, curry powder and egg. Season with salt and black pepper and mix until combined.
Shape the mixture into 10 to 12 golf-ball-size patties, just gently flattened, and lay them into a lightly greased baking dish or shallow non-stick baking sheet. Refrigerate for at least 15 minutes to firm up a little.
For the salsa: In a bowl, combine the pineapple, cilantro, mint, ginger, chile, lime juice and zest, and sugar. Toss well.
Just before cooking the frikkadels, brush the patties with a little olive oil. Transfer to the oven and bake until golden, 8 to 10 minutes. (If you'd like a crisper finish, then turn on the grill for the last 2 to 3 minutes.)
Serve immediately with the pineapple salsa on the side.