Add bananas, pecans, strawberries and pineapple to jello and stir to combine. Divide in half.
Pour half of jello mixture into a 12x18 pan. Refrigerate until set. Keep remaining jello at room temperature.
Spread sour cream evenly over jello in pan. Pour on remaining jello.
Cover and refrigerate until set, about 1 1/2 hours or overnight.