Put three spoons in the freezer.
Hull the strawberries and cut the larger ones in half.
Put the berries in a bowl and add 500 grams of sugar. Stir to coat and set aside.
Heat a heavy bottomed pot on low heat and add the oil. Add the chillies and cook for 10 minutes or until perfectly soft.
Add the sugared berries, the lemon zest and juice to the pot and stir.
Bring the mixture to a good boil for 20 minutes, stirring occasionally to ensure the jam doesn't stick. Watch that the pot doesn't overflow.
Add the remaining 250 grams of sugar and the salt. Stir to combine and continue to cook for another 20 minutes or until setting point.
While the jam is cooking, sterilise your jars. See Notes below.
Begin testing the jam for setting point 10 minutes after adding the second batch of sugar. The setting point of a jam or jelly is 105°C (221°F) so we can easily and accurately test using a thermometer. You can also use the frozen spoon method. Put a drop of jam on to one of the frozen spoons and allow to cool. If, when you drag your fingertip through the jam the path remains clean and doesn't fill with jam again, the jam is at setting point. This may take 30 - 40 minutes.
Carefully pour the jam in to the sterilised jars and seal with the lids. You can store this strawberry jam in the fridge straight away and it will keep for a few weeks but if you want to shelf store it for up to 12 months, you'll need to heat process your jars.