Place the strawberries in a medium saucepan with the lemon juice, maple syrup, vanilla, and sumac. Bring to a boil over medium heat, then reduce the heat and allow the mixture to simmer for 20 minutes, stirring often.
Once the strawberries are soft you can remove the mixture from the heat. Use a fork to mash up the strawberries.
Stir in the chia seeds and leave the jam to cool. As the jam cools the chia seeds will form a gel.
Once the jam is completely cool it can be transferred into a jar and kept in the fridge for up to a week.