This looks like the perfect summer treat!
1 kg fresh, seedless watermelon, skin removed & roughly chopped
1 tbsp freshly squeezed lime juice
1/4 tsp salt
1/4 tsp dried chili flakes
add watermelon, lime juice, salt & chili flakes into a food processor and blend until mixture forms a pulpy consistency
pass mixture through a sieve, pressing firmly through with the back of a spoon; discard remaining mixture from sieve
pour the sieved mixture into a wide metal baking tray or freezer-proof dish (make sure it will fit easily onto your freezer shelf) and freeze for approximately 2-3 hours or until ready to serve (mixture will keep in the freezer for 2-3 days)