Mix the rolled oats, 2 tablespoons chia seeds, and salt in a large bowl, breaking apart any compact chia with your fingertips.
Add the milk, Greek yogurt, 2 tablespoons maple syrup, and lemon zest. Stir for about 45 seconds, scraping the bottom and sides until no pockets of plain yogurt remain. Leave the bowl at room temperature for 10 minutes, then stir from the bottom for another 20 seconds, breaking up every visible chia clump.
Mash three-quarters of the blueberries in a medium bowl, leaving some small pieces. Stir in 1 tablespoon chia seeds, lemon juice, and 1 tablespoon maple syrup. Let stand for 5 minutes.
Divide half the oat base among four jars. Add the blueberry ripple, then cover with the remaining oat base. Drag a spoon through each jar once to create a broad swirl without fully mixing the colors.
Cover and refrigerate immediately for at least 6 hours or up to 4 days at 40°F or below.
Before eating, stir the chilled oats and add milk 1 tablespoon at a time if the jar feels too firm. Top with toasted almonds and optional fresh blueberries immediately before eating.