Mix Jell-O in two cups boiling water.
Add frozen strawberries (cut them into slices if they are big)
Add crushed pineapple and mashed banana to the gelatin, fruit mixture.
Pour 1/2 of the mixture into a 8"" X 10"" rectangular pan
Refrigerate this half of the mixture until it becomes solid (approximately 45 minutes)
Cover with sour cream
Slowly add the remaining fruit - gelatin mixture on top.
Refrigerate until hardened. (at least 1 - 2 hours)
Cut into squares to serve.
May add a dollop of whipped topping on top if desired