Place the frozen blueberries, lemon juice, and maple syrup in a small saucepan over medium heat. Keep stirring until they start to release some of their juices (this takes about 5-7 minutes). Then with either a fork or a potato masher, mash the blueberries.
Once you have your desired texture, stir in the chia seeds until well distributed and remove from the heat.
Transfer to a glass jar and let cool completely before putting on a tightly sealed lid. Store in the fridge for up to 10 days or in the freezer for 3 months.