Start by defrosting the mixed berries. (I used a triple berry blend of blackberries, blueberries, and raspberries.) You can let them defrost at room temperature, or you can speed this step up by defrosting them in the microwave.
Add the defrosted berries and juice to a medium-sized saucepan. Add the vegan honee or agave and stir to combine. Bring the mixture to a boil while stirring continuously.
Add the chia seeds and salt. Mix well to combine. Cook at a low boil for thirty minutes, stirring occasionally, until the jam is nicely reduced and thickened.
Carefully pour the thickened jam into a pint size mason jar, leaving about a half inch of room at the top. (Not all of the jam will fit so add the extra to a small bowl or container.) Screw on the lid and allow the jam to cool to room temperature, then store it in the refrigerator.