In a medium saucepan over medium heat, add the plums and cook until they start to break down, stirring and mashing frequently. Around 10 minutes or so.
Turn the heat to low, stir in the maple syrup and lemon juice. Then stir in the chia seeds and turn off the heat.
Allow the mixture to stand for 5 – 7 minutes until the chia seeds thicken the jam and mixture starts to cool down. The jam will keep thickening as it cools.
Serve immediately or transfer to an airtight container. Store in the fridge for up to 2 weeks.