Finely mash 2 bananas in a large bowl until very smooth. Stir in almond milk, oats, yogurt, walnuts, chia seeds, maple syrup, vanilla and cinnamon until evenly combined. Cover and refrigerate until thickened, 30 minutes to 1 hour.
Stir chocolate chips and coconut oil together in a small microwave-safe bowl. Microwave on Medium, stopping to stir every 20 seconds, until melted, about 45 seconds to 1 minute.
Divide the oat mixture among 4 (8-ounce) jars (about ½ cup each). Thinly slice the remaining banana. Layer half of the banana slices over the oat mixture in each jar, then top each with the remaining oat mixture; finish with the remaining banana slices. Spoon about 2 teaspoons of the melted chocolate chip mixture over each, tilting the jar to cover the entire surface.
Refrigerate, uncovered, until the chocolate layer is just set, about 20 minutes. Sprinkle with salt and cover. Refrigerate for at least 8 hours (or up to 4 days).
