Pre-heat your oven to gas mark 5 (190C/375F).
Get out an oven dish, I used a 40x27cm Pyrex roaster.
Combine together the white sugar, plain flour and vanilla extract.
Peel, core and separate your pineapple into chunks.
Wash the rhubarb and remove both ends.
Cut into one inch thick pieces.
Add the pineapple and rhubarb to your filling mixture.
Combine well.
Pour this into your oven dish.
Combine.
Pour into oven dish.
Combine together the four ingredients for your topping.
Rub together by hand until you have a crumble consistency.
Sprinkle this over the top of your rhubarb and pineapple mixture.
Bake for approximately 40 minutes, checking around 35 minutes to avoid burning the topping.
Serve and enjoy!