In a large bowl, mash bananas, add drained pineapple. Mix together.
Prepare jello as instructed except use only 1 cup of boiling water instead of the recommended 2 cups until dissolved. Then add 1 cup of cold water and add this to the bananas and pineapple. Stir in frozen strawberries and nuts to mixture until well blended.
Set bowl in fridge for 1 hour until thick. Pour 1/2 of the mixture into a 9x13 dish. Spread sour cream on top of mixture until covered. Pour the other 1/2 of mixture on top of sour cream and spread evenly. Refrigerate again until firm.