Prevent your screen from going dark
Prepare crust – preheat oven to 350°F (175°C). In a large bowl, mix graham cracker crumbs, sugar, and melted butter. Reserve 2 tablespoons of mixture, and press the rest into a 9×13-inch baking dish.
Bake crust – bake for 8-10 minutes until lightly golden. Remove from oven and set aside to cool.
Cook rhubarb – in a large saucepan, combine chopped rhubarb and water. Cook over medium-high heat until softened, 3-4 minutes. Stir in sugar, cornstarch, and strawberry jello until thickened and clear.
Assemble first layers – pour hot rhubarb mixture over cooled crust and top evenly with mini marshmallows. Refrigerate until completely set, about 2 hours.
Make pudding layer – in a large bowl, whisk together instant vanilla pudding mix and milk until thick. Gently fold in thawed whipped topping until smooth.
Finish bars – spread pudding mixture over set marshmallow layer. Sprinkle with reserved graham cracker crumbs. Refrigerate until completely set before slicing and serving.