In a medium pot, stir together the berries and maple syrup. Add a pinch of salt. Simmer over medium-high heat for 8-10 minutes until softened. Expect the berries to sweat a fair bit during this time, it's steamy in there.
Add the chia seeds and stir to combine. Continue simmering and stirring frequently (turn down the heat as necessary to prevent sticking) about 5-10 minutes longer, until most of the water cooks off and the jam is thickened.
Remove from heat and stir in lemon juice. Transfer the whole lot to a bowl and into the fridge, uncovered, until completely cool, at least two hours.
In a medium container stir together an entire can of coconut milk, oats, chia seeds, honey and cardamom until combined. Cover and chill for 1-2 hours, or overnight. The oats will soften and the mixture will thicken. Mix it up to combine before using.
Layer the mixed berry jam, overnight oats and sliced banana into small jars. Secure lids or cover with plastic wrap. The leftovers will keep in the fridge for up to 3-4 days. The jam will keep in an air-tight container in the fridge for up to 2 weeks. You can also freeze any leftover jam in freezer bags and thaw it for later use.