Combine the pineapple with juice, lemon juice, sugar and cinnamon in a medium saucepan. Cook over a medium heat, uncovered, stirring occasionally until the sugar is dissolved and the juice is reduced somewhat, about 3 minutes. Set aside to cool slightly.
Cut the bananas in half crosswise. Cut each banana half lengthwise, being careful not to cut all the way through. Split the banana halves open and place each one on a small dessert plate. Top each banana with a scoop of ice cream then about 2 1/2 tablespoons of the warm pineapple mixture. Top each with a mint leaf, if using, and serve.