Grease the slow cooker insert, then pour in the oats, water, bananas, chia seeds, and salt.

Cook on high for 2 to 3 hours or low for 6 to 8 hours. You can open the lid to stir occasionally, but that may increase the cook time.

Divide the oatmeal among 4 bowls. Top each one with chocolate chips, walnuts, and sliced banana. Drizzle with pure maple syrup if desired.