Preheat your oven to 350°F (175°C).
In a large mixing bowl, combine the chopped rhubarb, granulated sugar, cornstarch, and vanilla extract. Toss until the rhubarb is well coated.
Spread the mixture evenly in a greased 9x13-inch baking dish.
In another bowl, mix together the rolled oats, flour, shredded coconut, brown sugar, and salt.
Pour in the melted butter and stir until the mixture is crumbly.
Sprinkle this topping evenly over the rhubarb layer in the baking dish.
Bake in the preheated oven for 35-40 minutes, or until the topping is golden brown and the rhubarb is bubbly.
Allow to cool for at least 10 minutes before serving.