Combine the bananas, lemon juice, cream and sugar into a food processor and combine for 1 minute until smooth.
Remove ice cream bowl from the freezer and place into ice cream machine. Transfer banana mixture to the frozen bowl and add the walnuts, chocolate chunks and ½ the brownie bits. Freeze according to the manufactures directions. Carefully stir in remaining brownie bits at the end.
Remove ice cream from the bowl and place into a freezer safe container for at least 2 hours before serving.
Notes
Keep in mind that this will freeze very solidly. If you don't eat it all at once, you'll need to let it rest on the counter for a little bit before you are able to scoop.