Preheat your oven to 350°F (175°C).
In a large bowl, combine rhubarb, sugar, flour, and vanilla extract.
Pour the rhubarb mixture into a greased baking dish.
In another bowl, mix oats, brown sugar, flour, and cinnamon.
Add softened butter to the oat mixture and blend until crumbly.
Sprinkle the oat topping evenly over the rhubarb mixture.
Bake in the preheated oven for 45 minutes or until the topping is golden brown.
Remove from the oven and let it cool for about 10 minutes.
Serve warm, preferably with vanilla ice cream.
Enjoy your delicious rhubarb crisp!