Place strawberries in a small saucepan over medium heat.
Cook for 5 to 10 minutes, mashing frequently with a fork or potato masher, until the fruit has broken down into a chunky sauce.
Remove the saucepan from heat and stir in the chia seeds, sweetener, and lemon juice.
Allow the mixture to sit for 10 minutes, stirring occasionally, until the chia seeds expand and the jam thickens to the desired consistency.
Incorporate the vanilla extract once the jam has cooled slightly.
Transfer to a sterilized glass jar and store in the refrigerator for up to two weeks.