Using a fork, pierce potatoes all over. Set potatoes on plate and microwave on HIGH, turning every 5 min., until softened and cooked through, about 20 min. When cool enough to handle, slice in half lengthwise. Using a spoon, scoop the flesh into medium bowl (discard skins or reserve for another use). Mash and stir in 1 tsp (5 mL) coconut oil, pepper, 1/4 tsp (1 mL) salt and about 1/2 cup (125 mL) water, until potato mixture is soft and spreadable. (Note: For extra-crisped topping, also stir 2 tbsp (30 mL) butter into potato mixture.) Set aside.
Preheat broiler. In large saucepan, melt remaining coconut oil over medium heat. Whisk in flour and cook 1 min. Gradually whisk in coconut milk, 1 cup (250 mL) water, curry paste and remaining salt. Bring mixture to a bubble. Add fish, vegetables and oysters. Cook, stirring gently, until fish is cooked and vegetables are warmed through, 3 to 4 min.
Transfer fish mixture to 8 x 8-in. (20 x 20-cm) baking dish. Top with potato mixture. Place under broiler until top is golden brown and sauce is bubbling, 2 to 3 min. Serve with lime wedges.
Use green curry paste instead of red, or substitute Thai curry paste with equal amount of Indian curry paste.