In a bowl, toss the sliced bananas with the lemon juice to prevent browning; set aside until ready to use.
Option 1 - Mix lemon and orange JELL-O flavors together along with bananas, pineapple, and marshmallows. This option saves preparation time.
In a large bowl, mix together lemon and orange JELL-O. Add 2 cups boiling water and stir 2 minutes until dissolved. Stir in 1 1/2 cup cold water. Cover with plastic wrap and refrigerate for 1 hour to a soft-set gelatin mixture.
After 1 hour, remove gelatin mixture from the refrigerator and stir in the bananas and pineapple. Pineapple and bananas should look suspended or floating in the gelatin (it is fine for the marshmallows to float to the top). Pour the mixture into a glass serving bowl or a rectangular glass pan (you will be able to see the JELL-O and floating fruit). Cover with plastic wrap and refrigerate for at least 4 hours or overnight until the gelatin mixture in hard set.
Always store gelatin desserts in a covered container to avoid the formation of a thick rubbery skin on the surface.
Option 2 - Prepare separate layer for each JELL-O flavor and topping. I personally think this is the prettier way to serve this dish. I know, it takes more time to prepare - but if something is worth doing it is worth doing right!
In a medium-size bowl, dissolve the lemon gelatin in 1 cup boiling water, stirring for 2 minutes with a rubber spatula until all the crystals are dissolved. Stir in 3/4 cup of cold water. Cover with plastic wrap and refrigerate for 1 hour to a soft-set gelatin mixture.
After 1 hour, remove lemon gelatin mixture from the refrigerator and stir in the pineapple. Pineapple should look suspended or floating in the gelatin. Pour the pineapple gelatin mixture into a glass serving dish, cover with plastic wrap, and refrigerate for 4 hours until the gelatin mixture is hard set.
Once the lemon gelatin mixture is hard set, prepare the orange gelatin.
In a separate bowl, mix together the orange gelatin with 1 cup boiling water, stirring 2 minutes with a rubber spatula until all the crystal are dissolved. Stir in 3/4 cup of cold water. Add the miniature marshmallows and stir to combine (marshmallows will float to the top and this is fine). Gently spoon the orange gelatin mixture over the top of the hard-set lemon gelatin. You do not want to pour the orange gelatin mixture over the top of the lemon gelatin layer as it will create a hole in the lemon layer. This will also lose the nice layered effect separating each gelatin color. So - gently spoon!
Cover with plastic wrap and refrigerate for 1 hour to soft-set gelatin. After 1 hour, remove the orange gelatin from the refrigerator. Layer the top of the orange gelatin with the sliced bananas. Cover with plastic wrap and refrigerate 4 hours or overnight.
Store gelatin desserts in a covered container to avoid the formation of a thick rubbery skin on the surface.
Pineapple Topping - In a large saucepan over low heat, stir together the sugar, flour, reserved pineapple juice and beaten egg. Cook, stirring constantly, until the sauce just starts to boil and thicken(if cooked too quickly on high heat, the egg will separate). Immediately remove from heat when you see the sauce bubble up and start to rise. Pour the sauce into a small bowl, cover with plastic wrap, and let cool in the refrigerator (you can speed up the cooling time in the freezer for 1 hour).
Whipped Topping - In a separate mixing bowl on medium speed, beat together the whipped topping (or whipped cream) and cream cheese until soft peaks form. If making homemade whipping cream, add sugar to sweeten to taste. Set aside until ready to serve. Refrigerate if not serving immediately.
Option 3 - Pineapple mixture can be folded into the prepared Whipped Topping and then spread over the top of the gelatin.
Approximately 1 hour before serving, remove the gelatin dessert from the refrigerator. Spoon the Pineapple Topping over the top of the Gelatin Dessert, spreading evenly to cover. Then spread the Whipped Topping over the top of the Pineapple Topping until the top is completely covered.
Cover with plastic wrap and place back in the refrigerator until ready to serve. Sprinkle with grated cheddar cheese over the top for garnish right before serving.