Preheat oven to 375. In a mixing bowl, combine plums, sugar, flour, and the juice of 1 lime. Pour into the baking dish.
To make the crumble, combine oats, flour, brown sugar, salt, and butter. Cut with a pastry cutter until you see coarse crumbles. Pour crumbles on top of the plum mix.
Bake for 25-30 minutes or until golden and bubbly.