Wash the strawberries and discard leaves and stems. Halve the berries, cutting the large ones into quarters to make them all roughly the same size.
Combine all ingredients except the lemon juice in the slow cooker and stir to evenly mix.
Cover, but slightly vent the slow cooler, then cook on low until the mixture has thickened and is spreadable. This could take 10-12 hours, be sure to stir every hour or so.
Stir in the lemon juice and let cool with the lid off.
Store in sealable containers and store in the fridge for a week to 10 days. It can be stored for a few months in the freezer.