In a large skillet, heat 1 tablespoon oil over medium-high heat. Add half the garlic and ginger, and sauté 1 minute. Add shrimp, and cook, stirring frequently, until shrimp are pink and just cooked through; transfer to a plate.
Add the remaining oil, garlic, and ginger to the skillet, and sauté 1 minute over medium-high heat. Add tomatoes, curry powder, coriander, tamarind paste, sugar, turmeric, salt, and cayenne; cook 1 minute. Whisk in coconut milk, and heat to boiling; cook at a low boil, stirring occasionally, until reduced by half, about 10 minutes. Reduce the heat to low, and return shrimp to the skillet; cook for 2 minutes.
Just before serving, cut the risotto into individual “cakes,” shaped and sized as desired, using a cookie cutter or knife. Fry each cake in vegetable oil, turning to lightly brown the tops and bottoms. To serve, spoon some of the curry sauce onto each plate, arrange a risotto cake beside the sauce and top each with several shrimp, more sauce, the reserved sliced dark green onion, chopped cilantro, and if desired, toasted coconut.