In a medium saucepan, combine the chopped rhubarb, sugar, freshly squeezed lemon juice, and water. Over medium heat, simmer for 10-15 minutes, stirring occasionally, until the mixture thickens into a nice compote. Remove from heat and cool.

In a chilled mixing bowl, whip the heavy cream on medium speed for about 3-5 minutes until soft peaks form.

Gently fold the sweetened condensed milk into the whipped cream, then add the coarsely crushed granola and fold it in carefully.

Pour the cream mixture into a freezer-safe container and spoon the cooled rhubarb compote over the top, swirling gently to create a marbled effect.

Cover tightly and freeze for 4-6 hours or overnight until set.