Special equipment: Pastry bag and large star tip
In a large saucepan over medium heat, melt butter with water, salt and zest of 1 lime. Bring to a simmer and then slowly whisk in flour. Remove from heat and keep whisking until mixture forms a ball and breaks away from the sides of the pan. Slowly add eggs in thirds. Spoon batter into a pastry bag fitted with a large star tip and refrigerate 15 minutes. Meanwhile, fill a large saucepan 2/3 full with vegetable oil and heat to 350 degrees F. Remove batter from refrigerator and slowly squeeze 3-inch long strips of batter into the oil. Fry in batches, until golden brown, 5 to 6 minutes, flipping halfway through. Drain churros on paper towels. In a paper bag, add sugar, cinnamon and remaining zest. Once churros have cooled slightly, in batches, toss churros in bag and shake to coat with cinnamon sugar. Serve warm.