In a high-powered blender, combine the ripe bananas, stevia, and 3 cups (720 ml) of water.
Blend on high until the mixture is completely smooth and creamy.
Pour in the pineapple juice, frozen orange juice concentrate, and frozen lemon juice concentrate.
Blend again until all are fully incorporated.
Add the remaining 3 cups (720 ml) of water and give the mixture one final blend to ensure a consistent, smooth liquid.
Divide the base mixture evenly among three freezer-safe bottles or containers, leaving a little space at the top for expansion.
Freeze for at least 4 hours, or until firm.
When ready to serve, empty one bottle of the frozen slushy mix into a large punch bowl or pitcher. Slowly pour one liter of chilled ginger ale over the top and gently stir to combine, breaking up the frozen base.
Serve immediately and enjoy the fizz!