In a medium saucepan, combine water, butter, sugar, and salt. Bring to a boil over medium-high heat. Remove from heat and quickly stir in the flour, mixing vigorously until a smooth ball forms.

Let the dough cool for about 5 minutes. Add eggs one at a time, mixing well after each addition until smooth. Fold in mashed bananas.

Transfer dough to a piping bag fitted with a large star tip. Heat vegetable oil in a pot to 350°F (175°C).

Pipe 4-5 inch strips of dough into hot oil, cutting the end with scissors. Fry in small batches for about 2-3 minutes per side until golden brown.

Remove churros with a slotted spoon and place on paper towels to drain. Roll in cinnamon-sugar mixture while still hot.

For the dipping sauce, warm the dulce de leche to desired consistency and stir in mashed banana for an extra flavor boost.

Serve banana churros warm with a bowl of dulce de leche for dipping.