Melt one-half cup of the sugar over low heat until sugar forms a golden syrup. Stir constantly to prevent burning. Pour immediately into a shallow cake pan (8 × 8 × 2inches) or a nine-inch pie plate, turning and rolling pan from side to side to coat with caramel. Set aside.
Preheat oven to moderate (350°F.).
Combine three-quarters cup of the remaining sugar with the salt and cinnamon. Add pumpkin and eggs. Mix well. Stir in the evaporated milk, the water and vanilla extract. Mix well and turn into the caramel-coated pan. Set in a pan of hot water. Bake for one and one-quarter hours, or until a knife inserted into the center of the filling comes out clean. Cool and chill.
To serve, run a spatula around the sides of the pan. Turn flan out onto a serving plate. Cut into squares or wedges. Combine the whipped cream with the remaining sugar and the ginger and spread over the squares.