Take pineapple chunks, water, and sugar and lemon juice in a blender, blend them till it is smooth.
Strain the juice through strainer in a container in which you are going to freeze it.
Cover the container and freeze it for 2 hours. After two hours you find it starts to freeze from sides. Now using the fork break those ice crystals.
And freeze it again for 2 hours and repeat the same process for 2-3 times more. Then freeze it for longer time. And its ready to serve. Before serving keep the container out for 5 minutes and using fork scrap the granita and serve.
Straining process in optional. You can skip that step.
1 pineapple blended will make 1 litter pineapple juice. if your pineapple large or small adjust accordingly.