In a large bowl, mix lemon jello with boiling water until dissolved.

Add 7-Up to the jello mixture and stir well.

Refrigerate the jello mixture until it starts to slightly jell.

Gently fold in crushed pineapple, miniature marshmallows, and sliced bananas.

Pour the mixture into a serving dish and refrigerate until the jello is completely set.

In a saucepan, whisk together sugar, flour, egg, and pineapple juice.

Cook the mixture over medium heat, stirring constantly, until it thickens.

Remove the saucepan from heat and allow the mixture to cool slightly.

Stir in butter until melted and well combined.

Gently fold in non-dairy topping (or whipped cream if preferred).

Spread the topping evenly over the set jello salad.

Refrigerate the salad until chilled before serving.