Place oats,water, milk, salt, cinnamon, apricots, raisins maple syrup, and Banana in a baking dish deep enough to hold 2 quarts. Stir to combine. Place apples on top.
Fill slow cooker insert with enough water to come up half to 3/4 of side of baking dish.
Place casserole inside slow cooker. If you need more water to cover sides pour carefully on side of casserole dish. cover crockpot place on low. Cook 8 to 9 hours. Top with walnuts. Stir well and serve.