In a medium pot, stir together the berries, maple syrup and salt. Bring to a simmer over medium heat and cook for 5 minutes until the berries have softened.
Mash the berries (I like to use a potato masher) until mostly smooth.
Add the chia seeds and stir until combined. Simmer over medium heat, stirring frequently for 10-12 minutes, until the mixture has thickened.
Stir in the vanilla, lemon juice and lemon zest. Pour into a jar and refrigerate for at least 2 hours.
Jam will keep in the fridge for up to 2 weeks, or in the freezer for up to 2 months.