Begin by making the crumble. Add the flour, oats, brown sugar, cinnamon, nutmeg, and salt to a bowl and mix to combine. Pour in the melted butter and mix again until the crumble begins to clump up. If it is not clumping, add water 1 tablespoon at a time until the topping begins to clump. Set aside for now.
Preheat the oven to 400 degrees F.
Next make the filling. Add the chopped apples, plums, apricots, cranberries, and water into a large pot and heat over medium-high heat. Add the sugar to the pot with the cinnamon, nutmeg, and salt and toss to combine. Cook, stirring occasionally, for 15 minutes or until the fruit is beginning to soften and release liquid.
Mix the cornstarch into the orange juice to dissolve, then pour into the fruit mixture. Cook the fruit over medium-high heat for 2 minutes, or until the liquid has thickened. Remove from the heat and add the vanilla. Mix to combine.
Pour the fruit filling into a 9x13 inch baking dish and spread it out into an even layer. Sprinkle the crumble on top in an even layer, making sure to evenly distribute the clumps of crumble across the fruit.
Bake in the center of the oven for 30-40 minutes, until the crumble is golden brown and crisp. Let cool for 10 minutes before serving. Enjoy!