Mix first 6 ingredients together in a large bowl, stirring until sugar has dissolved.
Cover with plastic wrap, making sure the plastic wrap touches the top surface of the mixture to prevent a skin from forming on the top.
Refrigerate until thickened. (about 2 hours)
Meanwhile, dice the bananas into small pieces and drizzle with lemon juice (if using)
Arrange bananas on a baking sheet lined with parchment paper.
To prepare the ice cream, follow the manufacturer's instructions for your ice cream maker.
When ice cream is done churning, spoon it into an ice cream container.
Stir in crushed vanilla wafer cookies and fold in frozen bananas.
Place whole vanilla wafers on top for decoration if preferred.