Bring a pot of water to the boil. Meanwhile, peel and quarter the potatoes. Add the potatoes to the pot and boil on medium heat for 10-15 minutes or until tender. Remove from heat and drain. Move the boiled potatoes to a large bowl and mash until smooth. Set aside to cool.
Place the fish, fish sauce, red curry paste, lime zest and juice, chopped cilantro, spring onions, and egg into a food processor. Pulse until well combined. Add the mixture to the potatoes and mash until evenly distributed.
Shape the mixture into small patties and coat with breadcrumbs.
Heat the vegetable oil in a large frying pan over medium heat. Fry the fish cakes in batches for 2-3 minutes on each side, or until golden brown and cooked through. Drain on paper towels.
While the fish cakes are frying, prepare the sweet chili sauce. In a small saucepan, combine the sugar, water, rice vinegar, minced garlic, and chili flakes. Bring to a simmer and cook until the sugar has dissolved and the sauce has thickened slightly.
Serve the fish cakes hot with the sweet chili sauce on the side. Enjoy as a delicious meal or entree!