In a large saucepan, bring the water, milk, oil and salt to a boil. Add flour all at once and stir until a smooth ball forms. Transfer to a large bowl; let stand for 5 minutes. , Beat on medium-high speed for 1 minute or until the dough softens. Add egg and lemon zest; beat for 1-2 minutes. Set aside to cool. , In a deep cast-iron or heavy skillet, heat 1 in. oil to 375°. Insert a large star tip in a pastry bag; fill with dough. On a baking sheet, pipe dough into 4-in. strips. , Transfer strips to skillet and fry until golden brown on both sides. Drain on paper towels. Combine the sugar and cinnamon; sprinkle over churros. Serve warm.