Soak the noodles in hot water for 30 minutes, drain.
Meanwhile, slice the tofu into 1/4 inch blocks. Place the tofu between sheets of paper towels to soak up the excess liquid. (Ideally, place under something weighted to help extract more water. The more water that is removed, the more crispy the tofu will be)
In a small bowl, stir together the sugar, fish sauce, and vinegar.
Heat the oil over high heat until it begins to shimmer. Add the tofu and allow to fry 1-2 minutes (the tofu should be turning golden on the bottom). Turn the tofu over, then add the noodles and sauce. Stir constantly until the noodles absorb the sauce, about another minute.
Push aside the noodles and crack the egg into the empty space in the pan. Roughly scramble the egg, then toss it back in with the noodles while the egg is still soft. Remove the pan from the heat and toss in the bean sprouts and green onions. Stir to combine.
Transfer to a plate and serve.