Heat the oil in a large skillet over medium-high heat. Add the ginger and cook, stirring, until brown and crisp, about 7 minutes. Add the fish, stir gently until thoroughly mixed with the ginger and cook for about 3 minutes. Add the sugar, soy sauce, fish sauce and salt and stir well. Stir in the onion and cook for another 3 to 4 minutes. Add the red pepper and scallions and cook for another 2 minutes, then serve.