Heat 1 tablespoon oil in a medium saucepan over medium-high. Add curry paste; cook, stirring constantly, 1 minute. Add coconut milk and sugar; bring to a boil. Reduce to a simmer; cook until slightly thickened, about 5 minutes. Remove from heat; stir in lime juice and soy sauce. Heat 1 tablespoon oil in a large skillet over high. Add shrimp; cook until opaque, 4 to 5 minutes. Remove to a plate. Add remaining 1 tablespoon oil to pan. Add onion and bell pepper; cook, stirring often, until tender, 2 to 3 minutes. Add curry mixture, shrimp, pineapple, and 1/4 cup cilantro; cook until sauce is thickened, about 1 minute. Divide shrimp mixture evenly among 4 bowls. Top with scallions, peanuts, and remaining 1/4 cup cilantro.