1. In a saucepan, combine water, sugar, salt, and vegetable oil. Bring to a boil and remove from heat. Stir in flour until mixture forms a ball.
2. Heat oil for frying in a deep skillet to 375°F (190°C). Pipe strips of dough into hot oil using a piping bag. Fry until golden; drain on paper towels.
3. Combine 1 cup sugar and cinnamon. Roll drained churros in cinnamon and sugar mixture.
4. Assemble sundaes by placing churros in bowls, adding scoops of vanilla ice cream, drizzling with chocolate sauce, topping with whipped cream, and sprinkling with chopped nuts.