Place all of the ingredients except the toppings in the bottom of a 4-to-6-quart slow cooker
and stir to combine: Steel cut oats, water, milk, mashed bananas, flaxseed meal, vanilla, cinnamon, nutmeg, and salt. Cover and cook on low for 7-8 hours (overnight) or on high for 4 hours, until the oats are soft but maintain a bit of chew. Remove cover and stir to evenly combine the ingredients. Enjoy warm with desired toppings.