In 3-quart saucepan, heat oil (2 to 3 inches) over medium-high heat until thermometer inserted in oil reads 375 F
In small bowl, mix 3 tablespoons of the sugar and the cinnamon; set aside. In medium bowl, stir Bisquick mix, hot water and remaining 1 tablespoon sugar with spatula until dough forms.
Spoon dough into pastry bag fitted with 1/4-inch star tip. Pipe 5-inch strips of dough into hot oil. If necessary, cut dough with knife or scissors between each churro. Cook 2 to 3 minutes, turning frequently, until golden brown. Carefully remove from oil; drain on paper towels.
Immediately sprinkle churros generously with sugar-cinnamon mixture. Serve warm.